Different integration site structures between L1 protein-mediated retrotransposition in cis and retrotransposition in trans
© Kojima; licensee BioMed Central Ltd. 2010
Received: 28 January 2010
Accepted: 8 July 2010
Published: 8 July 2010
Long interspersed nuclear element-1 (LINE-1 or L1) is a dominant repetitive sequence in the human genome. Besides mediating its own retrotransposition, L1 can mobilize Alu and messenger RNA (mRNA) in trans, and probably also SVA and non-coding RNA. The structures of L1 copies and trans-mobilized retrocopies are variable and can be classified into three categories: full-length; 5'-truncated; and 5'-inverted insertions. These structures may be generated by different 5' integration mechanisms.
In this study, a method to correctly characterize insertions with short target site duplications (TSDs) is developed and extranucleotides, TSDs and microhomologies (MHs) at junctions were analysed for the three types of insertions. Only 5'-truncated L1 insertions were found to be associated with short TSDs. Both full-length and 5'-truncated retrotransposed sequences in trans, including Alu, SVA and mRNA retrocopies and also full-length and 5'-inverted L1, were not associated with short TSDs, indicating the difference of 5' attachment between retrotransposition in cis and retrotransposition in trans. Target sequence analysis suggested that short TSDs were generated in an L1 endonuclease-dependent manner. The MHs were longer for 5'-inverted L1 than for 5'-truncated L1, indicating less dependence on annealing in 5'-truncated L1 insertions.
The results suggest that insertions flanked by short TSDs occur more often coupled with the insertion of 5'-truncated L1 than with those of other types of insertions in vivo. The method used in this study can be used to characterize elements without any apparent boundary structures.
Long interspersed nuclear element-1 (LINE-1 or L1) is the only active non-long terminal repeat (non-LTR) retrotransposon family in humans and constitutes one sixth of the human genome [1, 2]. It encodes two proteins, open reading frame one protein (ORF1p) and open reading frame two protein (ORF2p). Both these proteins are essential for L1 retrotransposition . ORF2p contains two enzymatic domains: endonuclease (EN)  and reverse transcriptase (RT) . Retrotransposition-competent L1 copies are ~6000 bp in length [6, 7], but most of the L1 copies on the human genome are severely 5'-truncated [1, 8]. In addition, ~10% of the human L1 copies are rearranged to be composed of two segments: 5' inverted and 3' noninverted segments [9, 10]. L1 copies are classifiable into three categories: full-length; 5'-truncated; and 5'-inverted insertions.
5' inversion is most likely to be achieved by a variant of TPRT called twin priming [14–16] (Figure 1). In twin priming, one DNA end may be annealed to the 3'-terminus of L1 RNA as in standard retrotransposition, whereas the other end is annealed to the same L1 RNA internally. As the results of annealing, nucleotides derived from either the target DNA or L1 cDNA, called microhomologies (MHs), are often observed at the 5'- and the 3'-ends of 5'-inverted L1 copies. After reverse transcription, L1 RNA could be degraded and the two cDNA strands are annealed at a region of short complementarity. This annealing was presumed on the basis of MHs at the inversion junction.
Template jumping, proposed from the analysis of another non-LTR retrotransposon family R2 [17–20], is a most likely mechanism for the generation of full-length L1 copies  (Figure 1). In the template jumping model, the RT molecule synthesizing first-strand cDNA jumps to the 3'-end of the target DNA in order to continue DNA polymerization.
The mechanism for 5' integration of 5'-truncated L1 copies has long been debated and various mechanisms for the 5' attachment have been proposed (Figure 1). Template jumping could contribute to 5'-truncated retrotransposition as well as to full-length retrotransposition [19, 21]. The double TPRT model proposed that annealing of the internal sequence of cDNA with the 5' target site terminates reverse transcription and enhances second strand cDNA synthesis [15, 22, 23]. Reverse transcription termination before the completion could generate a Y-shaped intermediate, which could be healed by cellular DNA repair mechanisms, including microhomology-mediated end-joining (MMEJ) and non-homologous end-joining (NHEJ) [16, 24–26].
Proteins encoded by L1, as well as other LINEs contribute to short interspersed nuclear element (SINE) mobilization [27, 28]. There are two active SINE families, Alu and SVA, in the human genome [1, 29]. Alu can be mobilized by L1 ORF2 proteins in the absence of L1 ORF1p [27, 30]. This indicates that the retrotransposition mechanisms of L1 and Alu are not completely identical. SVA is a composite SINE containing fragments derived from Alu and human endogenous retrovirus (HERV)-K10 [29, 31, 32]; it is also considered to be mobilized depending on the L1 machinery.
Human L1 and Alu are usually flanked by ~15-bp TSDs [9, 33, 34]. TSDs are used to determine the junctions of L1 insertions in genome-wide screening . However, in the case of short TSDs, an accidental sequence match covers true TSDs. Target analysis of nested transposons (TANT) is a method to characterize LINE insertions with short TSDs. It is, however, limited by the low copy number of insertions nested in other transposons [34–36]. The advantage of this method is its ability to assume pre-inserted empty sites. Pre-inserted sequences can also be characterized by analysing orthologous sequences of outgroup species.
In this study, human-specific insertions and chimpanzee-specific insertions of L1, Alu, SVA and non-coding RNA (ncRNA) retrocopies were characterized by a newly developed method that can distinguish insertions from deletions and can characterize insertions with short TSDs. Only 5'-truncated L1 insertion is associated with short TSDs. Different target site structures were found on 5'-truncated retrotranspositions in cis and retrotranspositions in trans.
Precise characterization of retrotransposon insertions with extranucleotides and/or flanked by short TSDs
In this study, 6197 human-specific insertions and 2910 chimpanzee-specific insertions which satisfied all the following criteria were found: (1) length between 50 bp and 10,000 bp; (2) ≥5-bp direct repeats at both junctions; (3) not a part of segmental duplications; (4) not inserted in repetitive sequences; and (5) orthologous locus can be determined in either orangutan or macaque. Criteria 1-3 were applied in order to enrich the insertions of LINEs and SINEs. Criterion 4 was applied because the orthologous locus in orangutans and macaques could not be characterized for insertions inside of repetitive sequences. Criterion 5 was used to distinguish species-specific insertions from species-specific deletions.
Two primate genomes were used as outgroups to characterize the pre-inserted empty sites for each insertion; the orangutan and macaque genomes were complementary. Although empty sites for 3927 human-specific insertions and for 1281 chimpanzee-specific insertions were identified in the genomes of both species, empty sites for 2270 human-specific insertions and for 1629 chimpanzee-specific insertions were found only in the genome of either orangutan or macaque.
Repertories of human-specific insertions and chimpanzee-specific insertions
Human-specific and chimpanzee-specific insertions with ≥5bp TSDs
HERV and solo LTR
The origins of the ncRNA retrocopies were ribosomal RNA (rRNA), small nuclear RNA (snRNA), small nucleolar RNA (snoRNA), transfer RNA (tRNA), 7SK RNA, and 7SL RNA (Additional File 1). Among 25 ncRNA retrocopies, only three contained polyA tails. These three could be retrocopies generated by template switching during the very beginning of reverse transcription [41, 42]. The remaining 22 retrocopies were usually 3'-truncated and similar to the tailless retropseudogenes reported by Schmitz et al. . Tailless retropseudogenes were originally reported as retrocopies of tRNA that are 3'-truncated, without A-rich tails, and flanked by TSDs. They also detected tailless retrocopies of rRNAs and snRNAs. Tailless retrocopies of snoRNAs, 7SK RNA and 7SL RNA are reported for the first time here, indicating that all ncRNAs can become templates of tailless retrocopies.
Frequent existence of 5' extranucleotides in full-length L1 retrotransposition
The 5'-terminal heterogeneity of L1 was first analysed because the insertion junction could be determined without ambiguity. Among the factors causing heterogeneous 5' ends of L1 [44, 45], Yin Yang 1 (YY1) transcription factor binding to L1 nucleotides 12-22 (CAAGATGGCCG) could direct transcription to initiate at heterogeneous purine residues located near the 5'-end of L1.
5' inversion occurred frequently with L1 retrotransposition but rarely with Alu and SVA retrotransposition
Three types of L1 insertions in human and chimpanzee
Three types of Alu insertions in human and chimpanzee
As the 5'-end of SVA is composed of variable numbers of degenerate CCCTCT repeats , full-length and 5'-truncated SVAs could not be distinguished correctly. Among 477 SVA insertions, 95 started with G followed by degenerated CCCTCT repeats. Some of them are likely to be full-length insertions with a reverse-transcribed 5'-cap, like full-length L1 insertions . Only four instances of 5'-inverted SVA insertions were found (Additional File 2). The 5'-inverted SVA insertion showed a structure similar to inverted L1, mRNA retrocopies and Alu. The proportion of the 5'-inverted SVA (4/477 = 0.84%) was very small.
5'-inverted L1 was rarely inserted with extranucleotides at the 5' junctions
The frequency of insertions with 5' extranucleotides
Type of insertion
No. of insertions with extranucleotides
5'-truncated L1 copies were sometimes accompanied by short TSDs
The TSD length distribution of full-length L1 was similar to that considered true for L1. The peak length was 14-16 bp, and there was a small number of L1 with short TSDs (Figure 3A). These results support the ability of the analysis to characterize insertions with short TSD length precisely.
Chi-square or Fisher's exact test for the frequency of ≤ 9-bp target site duplications
5'-truncated L1 > full-length L1
5'-truncated L1 > 5'-inverted L1
5'-truncated L1 > full-length Alu
5'-truncated L1 > 5'-truncated Alu
5'-truncated L1 > 5'-truncated SVA
5'-truncated L1 > 5'-truncated mRNA retrocopy
Short TSDs observed in 5'-truncated L1 copies were likely dependent on endonuclease
Short target site duplications (TSDs) with or without allowing nucleotide substitutions
5-bp TSD in relaxed criterion*/
5-bp TSD in strict criterion*
6-bp TSD in relaxed criterion*/
6-bp TSD in strict criterion*
MH length distribution at 5' junctions
Next 5' MHs were analysed. Full-length L1 insertions showed MH length distribution predicted as if each of four nucleotides was observed by chance (Figure 3C), consistent with the previous study .
Chi-square or Fisher's exact test for the frequency of ≥1-bp microhomologies (MHs)
5'-inverted L1 > 5'-truncated L1
5'-truncated L1 > Full-length L1
5'-truncated L1 > 5'-truncated Alu
5' junction of 5'-inverted L1 > Inversion junction of 5'-inverted L1
Inversion junction of 5'-inverted L1 > 5' junction of full-length L1
5'-truncated L1 > 5'-truncated SVA
5'-truncated L1 > 5'-truncated mRNA retrocopies
Full-length Alu insertions were similar to full-length L1 insertions in terms of the frequency of MHs (Figure 3C). 5'-truncated Alu showed a weak dependence on MHs. However, the frequency of MHs in 5'-truncated Alu was not as high as that in 5'-truncated L1 (Table 7). In summary, the frequency of MHs was in the order full-length L1 ≈ full-length Alu < 5'-truncated Alu < 5'-truncated L1 < 5'-inverted L1.
MH length distribution of inversion junctions and 3' junctions
The MH length distribution at the inversion junction of 5'-inverted L1 was similar to that at the 5' junction of 5'-truncated L1 (Figure 3D). The frequency of insertions without MHs at the inversion junction of 5'-inverted L1 was higher than that at the 5' junction of 5'-inverted L1 and lower than that at the 5' junction of full-length L1 (Table 7).
The MH length distribution at the 3' junctions of endonuclease-independent L1 retrotransposition  and tailless retrocopies of tRNAs  was investigated (Figure 3D). The distributions of 3' MHs of endonuclease-independent L1 retrotransposition and tailless retrocopies were similar to those of the 5' MHs of 5'-inverted L1, especially in terms of the frequency of short MHs. The large peak at 3 bp in the 3' junctions of endonuclease-independent L1 insertions is likely due to its small data set.
SVA and mRNA retrocopy showed similar length distribution of TSDs and MHs as Alu
Figure 3B and 3D show the distributions of TSDs and MHs at the 5' junctions of 5'-truncated SVA and 5'-truncated mRNA retrocopy insertions. It is clear that short TSDs were rarely associated with insertions of 5'-truncated SVA and 5'-truncated mRNA retrocopies (Figure 3B). Because of the small sample sizes, Fisher's exact test, not chi-square test, was used to show statistical significance for the difference (Table 5). The order of frequency of insertion with ≤ 9-bp TSDs were 5'-truncated L1 > 5'-truncated SVA ≈ 5'-truncated mRNA retrocopy. The frequency of insertions without MHs was higher for the 5'-truncated SVA and 5'-truncated mRNA retrocopies than for 5'-truncated L1 (Figure 3D; Table 7). In summary, the length distributions of both TSDs and MHs associated with insertions of 5'-truncated SVA and 5'-truncated mRNA retrocopies were similar to those associated with 5'-truncated Alu insertions and dissimilar to those associated with 5'-truncated L1.
No correlation between TSD length and MHs
As the length distributions of TSDs and MHs are distinguishable features between retrotransposition in cis and retrotransposition in trans, one can speculate that short TSDs are dependent on the long MHs. However, there was no correlation between TSD length and the existence of MHs (data not shown).
Short TSDs specifically associated with 5'-truncated L1
The most significant finding in this study was that a bias towards shorter TSDs in truncated L1s, although insertions with longer TSDs still predominate even in the 5'-truncated elements. The TSD length distribution of 5'-truncated L1 was different from those of full-length and 5'-inverted L1. In the retrotransposition assay in HeLa cells performed by Gilbert et al. , all 6 full-length and 17 5'-inverted L1 insertions were flanked with TSDs of 10-17 bp, whereas 5'-truncated L1 insertions were frequently coupled with radical alteration of the target sites, including extremely long TSDs, target site deletions, and short TSDs of < 10 bp. These radical alterations were considered to be due to peculiarities associated with HeLa cells, but the present analysis showed that at least short TSDs are actually coupled with 5'-truncated L1 insertions in vivo. TSDs only between 5 bp and 30 bp in length were collected in this study, and further study to characterize shorter and longer TSDs is needed to clarify other radical alterations in vivo.
Difference in 5'-truncated insertion between in cis and in trans
5'-truncated retrotransposition in trans is not associated with short TSDs. What causes the difference between retrotransposition in cis and retrotransposition in trans? There have been many papers describing the differences between L1 and Alu retrotransposition [27, 30, 48]. However, SVA and mRNA retrocopies showed TSD length distributions similar to Alu. Therefore, the binding ability to signal recognition particles  and the type of RNA polymerase  can be excluded from the answer to this question.
It is difficult to propose a model from the data described here, but one possible explanation is that the longer time for reverse transcription of L1 RNA, longer than other RNAs, would attract cellular DNA repair machineries. Gilbert et al.  proposed abortive retrotransposition generates Y-branched intermediate and it is probably healed by microhomology-mediated end joining to generate the radical alteration of insertion sites. When the top strand is cleaved before the completion of first-strand cDNA synthesis, the L1 retrotransposition intermediate constitutes a DNA double-strand break . From the observation of few 5' inversion in trans-mobilized elements, top strand cleavage before the completion of first-strand cDNA synthesis could be nearly an exclusive feature of L1 retrotransposition  and possibly increases the 5' rejoining by cellular DNA repair system.
In this study, large-scale identification of retrotransposon insertions was achieved. Only closely related genomic sequences and at least one genomic sequence as an obvious outgroup were needed for analysis. One important improvement is that insertions could be distinguished from deletions, enabling the characterization of insertions with no signatures, and with drastic rearrangements.
The TSD length analysed in this study was restricted between 5 and 30 bp because of the limit of the computational power and manual adjustment, but all insertions with or without TSDs could be characterized in the method developed in this study. TSDs of L1 and trans-mobilized elements by L1 are relatively long among the transposable elements. Many non-LTR retrotransposons show shorter TSDs , DNA transposons and LTR retrotransposons show much shorter TSDs, and Helitrons show no TSDs . The method used in this study has the power to characterize these elements systematically and independently of TSD length.
The newly developed method using outgroup genome sequences can distinguish insertions from deletions and can characterize insertions with short TSDs correctly. This method can be applied to characterize elements without any obvious boundary structures. This study confirmed the present knowledge of L1-dependent retrotransposition, and revealed the relatively frequent appearance of short TSDs coupled with 5'-truncated L1 in vivo.
Materials and methods
Genome sequences of human, common chimpanzee, Sumatran orangutan, and rhesus macaque and the pairwise alignment between human and chimpanzee genomes were downloaded from the University of California, Santa Cruz Genome Browser website .
Characterization of species-specific insertions and TSDs
Human- and chimpanzee-specific insertions were collected as described previously . L1, Alu and SVA insertions were characterized by using RepeatMasker  with a library including only three human repetitive sequences: L1.3 (DDBJ/EMBL/Genbank accession number: L19088), Alu Y  and SVA . RepeatMasker was also run with the repeat library downloaded from RepBase  in order to characterize ncRNAs and endogenous retroviruses. Insertions including more than two types of insertions were manually excluded, with the exception of insertions in which 3'-transduced sequences could be characterized on the basis of large sequence variation from the consensus. Insertions with nested insertions, deletions, or duplications inside of the elements were also excluded.
Analysis of target sequences
Sequence logos of the target sequences were generated by using WebLogo .
Analysis of MH length
To identify MHs at 5' junctions, RepeatMasker was used with two different queries; one included only sequences of inserts and the other included sequences of both inserts and TSDs. If repetitive elements were extended into TSDs, the extended sequences were considered to be MHs. Nucleotides corresponding to both inverted and noninverted segments of repetitive elements were counted as MHs at inversion junctions, and the MHs at 3' junctions were manually counted in the published data sets [43, 47]. Sen et al.  reported 11 3' junction sequences of endonuclease-independent L1 insertions, and Schmitz et al.  reported 238 3' junction sequences of tailless retrocopies of tRNA.
bona fide 5'-truncated SVA insertions were obtained by collecting SVA insertions without CCCTCT repeats. Consequently, 91 5'-truncated SVA insertions were found. In the case of mRNA retrocopies, because the transcription start site is considered to be heterogeneous, the retrocopies starting at > 50 bp downstream from the +1 position of annotated transcripts were considered as 5'-truncated mRNA retrocopies, and 53 5'-truncated retrocopies were identified.
human endogenous retrovirus
long interspersed nuclear element
long terminal repeat
microhomology-mediated end joining
nonhomologous end joining
open reading frame 1 protein
open reading frame 2 protein
short interspersed nuclear element
target-primed reverse transcription
target site duplication
target analysis of nested transposons.
The author thanks Dr Norihiro Okada for the useful comments and suggestions. This work was supported by grants from the Ministry of Education, Culture, Sports, Science, Technology. KKK was the recipient of a Grant-in-Aid from the Japan Society for the Promotion of Science for Young scientists.
- Lander ES, Linton LM, Birren B, Nusbaum C, Zody MC, Baldwin J, Devon K, Dewar K, Doyle M, FitzHugh W: Initial sequencing and analysis of the human genome. Nature. 2001, 409 (6822): 860-921. 10.1038/35057062.View ArticlePubMedGoogle Scholar
- Brouha B, Schustak J, Badge RM, Lutz-Prigge S, Farley AH, Moran JV, Kazazian HH: Hot L1s account for the bulk of retrotransposition in the human population. Proc Natl Acad Sci USA. 2003, 100 (9): 5280-5285. 10.1073/pnas.0831042100.PubMed CentralView ArticlePubMedGoogle Scholar
- Moran JV, Holmes SE, Naas TP, DeBerardinis RJ, Boeke JD, Kazazian HH: High frequency retrotransposition in cultured mammalian cells. Cell. 1996, 87 (5): 917-927. 10.1016/S0092-8674(00)81998-4.View ArticlePubMedGoogle Scholar
- Feng Q, Moran JV, Kazazian HH, Boeke JD: Human L1 retrotransposon encodes a conserved endonuclease required for retrotransposition. Cell. 1996, 87 (5): 905-916. 10.1016/S0092-8674(00)81997-2.View ArticlePubMedGoogle Scholar
- Mathias SL, Scott AF, Kazazian HH, Boeke JD, Gabriel A: Reverse transcriptase encoded by a human transposable element. Science. 1991, 254 (5039): 1808-1810. 10.1126/science.1722352.View ArticlePubMedGoogle Scholar
- Scott AF, Schmeckpeper BJ, Abdelrazik M, Comey CT, O'Hara B, Rossiter JP, Cooley T, Heath P, Smith KD, Margolet L: Origin of the human L1 elements: proposed progenitor genes deduced from a consensus DNA sequence. Genomics. 1987, 1 (2): 113-125. 10.1016/0888-7543(87)90003-6.View ArticlePubMedGoogle Scholar
- Dombroski BA, Mathias SL, Nanthakumar E, Scott AF, Kazazian HH: Isolation of an active human transposable element. Science. 1991, 254 (5039): 1805-1808. 10.1126/science.1662412.View ArticlePubMedGoogle Scholar
- Grimaldi G, Skowronski J, Singer MF: Defining the beginning and end of KpnI family segments. EMBO J. 1984, 3 (8): 1753-1759.PubMed CentralPubMedGoogle Scholar
- Szak ST, Pickeral OK, Makalowski W, Boguski MS, Landsman D, Boeke JD: Molecular archeology of L1 insertions in the human genome. Genome Biol. 2002, 3 (10): research0052-10.1186/gb-2002-3-10-research0052.PubMed CentralView ArticlePubMedGoogle Scholar
- Kazazian HH, Moran JV: The impact of L1 retrotransposons on the human genome. Nat Genet. 1998, 19 (1): 19-24. 10.1038/ng0598-19.View ArticlePubMedGoogle Scholar
- Luan DD, Korman MH, Jakubczak JL, Eickbush TH: Reverse transcription of R2Bm RNA is primed by a nick at the chromosomal target site: a mechanism for non-LTR retrotransposition. Cell. 1993, 72 (4): 595-605. 10.1016/0092-8674(93)90078-5.View ArticlePubMedGoogle Scholar
- Cost GJ, Feng Q, Jacquier A, Boeke JD: Human L1 element target-primed reverse transcription in vitro. Embo J. 2002, 21 (21): 5899-5910. 10.1093/emboj/cdf592.PubMed CentralView ArticlePubMedGoogle Scholar
- Cost GJ, Boeke JD: Targeting of human retrotransposon integration is directed by the specificity of the L1 endonuclease for regions of unusual DNA structure. Biochemistry. 1998, 37 (51): 18081-18093. 10.1021/bi981858s.View ArticlePubMedGoogle Scholar
- Ostertag EM, Kazazian HH: Twin priming: a proposed mechanism for the creation of inversions in L1 retrotransposition. Genome Res. 2001, 11 (12): 2059-2065. 10.1101/gr.205701.PubMed CentralView ArticlePubMedGoogle Scholar
- Symer DE, Connelly C, Szak ST, Caputo EM, Cost GJ, Parmigiani G, Boeke JD: Human l1 retrotransposition is associated with genetic instability in vivo. Cell. 2002, 110 (3): 327-338. 10.1016/S0092-8674(02)00839-5.View ArticlePubMedGoogle Scholar
- Gilbert N, Lutz S, Morrish TA, Moran JV: Multiple fates of L1 retrotransposition intermediates in cultured human cells. Mol Cell Biol. 2005, 25 (17): 7780-7795. 10.1128/MCB.25.17.7780-7795.2005.PubMed CentralView ArticlePubMedGoogle Scholar
- Bibillo A, Eickbush TH: The reverse transcriptase of the R2 non-LTR retrotransposon: continuous synthesis of cDNA on non-continuous RNA templates. J Mol Biol. 2002, 316 (3): 459-473. 10.1006/jmbi.2001.5369.View ArticlePubMedGoogle Scholar
- Bibillo A, Eickbush TH: End-to-end template jumping by the reverse transcriptase encoded by the R2 retrotransposon. J Biol Chem. 2004, 279 (15): 14945-14953. 10.1074/jbc.M310450200.View ArticlePubMedGoogle Scholar
- Stage DE, Eickbush TH: Origin of nascent lineages and the mechanisms used to prime second-strand DNA synthesis in the R1 and R2 retrotransposons of Drosophila. Genome Biol. 2009, 10 (5): R49-10.1186/gb-2009-10-5-r49.PubMed CentralView ArticlePubMedGoogle Scholar
- Kurzynska-Kokorniak A, Jamburuthugoda VK, Bibillo A, Eickbush TH: DNA-directed DNA polymerase and strand displacement activity of the reverse transcriptase encoded by the R2 retrotransposon. J Mol Biol. 2007, 374 (2): 322-333. 10.1016/j.jmb.2007.09.047.PubMed CentralView ArticlePubMedGoogle Scholar
- Babushok DV, Ostertag EM, Courtney CE, Choi JM, Kazazian HH: L1 integration in a transgenic mouse model. Genome Res. 2006, 16 (2): 240-250. 10.1101/gr.4571606.PubMed CentralView ArticlePubMedGoogle Scholar
- Voliva CF, Martin SL, Hutchison CA, Edgell MH: Dispersal process associated with the L1 family of interspersed repetitive DNA sequences. J Mol Biol. 1984, 178 (4): 795-813. 10.1016/0022-2836(84)90312-7.View ArticlePubMedGoogle Scholar
- Martin SL, Li WL, Furano AV, Boissinot S: The structures of mouse and human L1 elements reflect their insertion mechanism. Cytogenet Genome Res. 2005, 110 (1-4): 223-228. 10.1159/000084956.View ArticlePubMedGoogle Scholar
- Morrish TA, Gilbert N, Myers JS, Vincent BJ, Stamato TD, Taccioli GE, Batzer MA, Moran JV: DNA repair mediated by endonuclease-independent LINE-1 retrotransposition. Nat Genet. 2002, 31 (2): 159-165. 10.1038/ng898.View ArticlePubMedGoogle Scholar
- Zingler N, Willhoeft U, Brose HP, Schoder V, Jahns T, Hanschmann KM, Morrish TA, Lower J, Schumann GG: Analysis of 5' junctions of human LINE-1 and Alu retrotransposons suggests an alternative model for 5'-end attachment requiring microhomology-mediated end-joining. Genome Res. 2005, 15 (6): 780-789. 10.1101/gr.3421505.PubMed CentralView ArticlePubMedGoogle Scholar
- Suzuki J, Yamaguchi K, Kajikawa M, Ichiyanagi K, Adachi N, Koyama H, Takeda S, Okada N: Genetic evidence that the non-homologous end-joining repair pathway is involved in LINE retrotransposition. PLoS Genet. 2009, 5 (4): e1000461-10.1371/journal.pgen.1000461.PubMed CentralView ArticlePubMedGoogle Scholar
- Dewannieux M, Esnault C, Heidmann T: LINE-mediated retrotransposition of marked Alu sequences. Nat Genet. 2003, 35 (1): 41-48. 10.1038/ng1223.View ArticlePubMedGoogle Scholar
- Kajikawa M, Okada N: LINEs mobilize SINEs in the eel through a shared 3' sequence. Cell. 2002, 111 (3): 433-444. 10.1016/S0092-8674(02)01041-3.View ArticlePubMedGoogle Scholar
- Ostertag EM, Goodier JL, Zhang Y, Kazazian HH: SVA elements are nonautonomous retrotransposons that cause disease in humans. Am J Hum Genet. 2003, 73 (6): 1444-1451. 10.1086/380207.PubMed CentralView ArticlePubMedGoogle Scholar
- Wallace N, Wagstaff BJ, Deininger PL, Roy-Engel AM: LINE-1 ORF1 protein enhances Alu SINE retrotransposition. Gene. 2008, 419 (1-2): 1-6. 10.1016/j.gene.2008.04.007.PubMed CentralView ArticlePubMedGoogle Scholar
- Bennett EA, Coleman LE, Tsui C, Pittard WS, Devine SE: Natural genetic variation caused by transposable elements in humans. Genetics. 2004, 168 (2): 933-951. 10.1534/genetics.104.031757.PubMed CentralView ArticlePubMedGoogle Scholar
- Wang H, Xing J, Grover D, Hedges DJ, Han K, Walker JA, Batzer MA: SVA elements: a hominid-specific retroposon family. J Mol Biol. 2005, 354 (4): 994-1007. 10.1016/j.jmb.2005.09.085.View ArticlePubMedGoogle Scholar
- Jurka J: Sequence patterns indicate an enzymatic involvement in integration of mammalian retroposons. Proc Natl Acad Sci USA. 1997, 94: 1872-1877. 10.1073/pnas.94.5.1872.PubMed CentralView ArticlePubMedGoogle Scholar
- Ichiyanagi K, Okada N: Genomic alterations upon integration of zebrafish L1 elements revealed by the TANT method. Gene. 2006, 383: 108-116. 10.1016/j.gene.2006.07.038.View ArticlePubMedGoogle Scholar
- Ichiyanagi K, Nakajima R, Kajikawa M, Okada N: Novel retrotransposon analysis reveals multiple mobility pathways dictated by hosts. Genome Res. 2007, 17 (1): 33-41. 10.1101/gr.5542607.PubMed CentralView ArticlePubMedGoogle Scholar
- Ichiyanagi K, Okada N: Mobility pathways for vertebrate L1, L2, CR1, and RTE clade retrotransposons. Mol Biol Evol. 2008, 25 (6): 1148-1157. 10.1093/molbev/msn061.View ArticlePubMedGoogle Scholar
- Mills RE, Bennett EA, Iskow RC, Luttig CT, Tsui C, Pittard WS, Devine SE: Recently mobilized transposons in the human and chimpanzee genomes. Am J Hum Genet. 2006, 78 (4): 671-679. 10.1086/501028.PubMed CentralView ArticlePubMedGoogle Scholar
- Lee J, Cordaux R, Han K, Wang J, Hedges DJ, Liang P, Batzer MA: Different evolutionary fates of recently integrated human and chimpanzee LINE-1 retrotransposons. Gene. 2007, 390 (1-2): 18-27. 10.1016/j.gene.2006.08.029.PubMed CentralView ArticlePubMedGoogle Scholar
- Gilbert N, Lutz-Prigge S, Moran JV: Genomic deletions created upon LINE-1 retrotransposition. Cell. 2002, 110 (3): 315-325. 10.1016/S0092-8674(02)00828-0.View ArticlePubMedGoogle Scholar
- Kojima KK, Okada N: mRNA retrotransposition coupled with 5' inversion as a possible source of new genes. Mol Biol Evol. 2009, 26 (6): 1405-1420. 10.1093/molbev/msp050.View ArticlePubMedGoogle Scholar
- Buzdin A, Gogvadze E, Kovalskaya E, Volchkov P, Ustyugova S, Illarionova A, Fushan A, Vinogradova T, Sverdlov E: The human genome contains many types of chimeric retrogenes generated through in vivo RNA recombination. Nucleic Acids Res. 2003, 31 (15): 4385-4390. 10.1093/nar/gkg496.PubMed CentralView ArticlePubMedGoogle Scholar
- Garcia-Perez JL, Doucet AJ, Bucheton A, Moran JV, Gilbert N: Distinct mechanisms for trans-mediated mobilization of cellular RNAs by the LINE-1 reverse transcriptase. Genome Res. 2007, 17 (5): 602-611. 10.1101/gr.5870107.PubMed CentralView ArticlePubMedGoogle Scholar
- Schmitz J, Churakov G, Zischler H, Brosius J: A novel class of mammalian-specific tailless retropseudogenes. Genome Res. 2004, 14 (10a): 1911-1915. 10.1101/gr.2720104.PubMed CentralView ArticlePubMedGoogle Scholar
- Athanikar JN, Badge RM, Moran JV: A YY1-binding site is required for accurate human LINE-1 transcription initiation. Nucleic Acids Res. 2004, 32 (13): 3846-3855. 10.1093/nar/gkh698.PubMed CentralView ArticlePubMedGoogle Scholar
- Lavie L, Maldener E, Brouha B, Meese EU, Mayer J: The human L1 promoter: variable transcription initiation sites and a major impact of upstream flanking sequence on promoter activity. Genome Res. 2004, 14 (11): 2253-2260. 10.1101/gr.2745804.PubMed CentralView ArticlePubMedGoogle Scholar
- Crooks GE, Hon G, Chandonia JM, Brenner SE: WebLogo: a sequence logo generator. Genome Res. 2004, 14 (6): 1188-1190. 10.1101/gr.849004.PubMed CentralView ArticlePubMedGoogle Scholar
- Sen SK, Huang CT, Han K, Batzer MA: Endonuclease-independent insertion provides an alternative pathway for L1 retrotransposition in the human genome. Nucleic Acids Res. 2007, 35 (11): 3741-3751. 10.1093/nar/gkm317.PubMed CentralView ArticlePubMedGoogle Scholar
- Kroutter EN, Belancio VP, Wagstaff BJ, Roy-Engel AM: The RNA polymerase dictates ORF1 requirement and timing of LINE and SINE retrotransposition. PLoS Genet. 2009, 5 (4): e1000458-10.1371/journal.pgen.1000458.PubMed CentralView ArticlePubMedGoogle Scholar
- Gasior SL, Wakeman TP, Xu B, Deininger PL: The human LINE-1 retrotransposon creates DNA double-strand breaks. J Mol Biol. 2006, 357 (5): 1383-1393. 10.1016/j.jmb.2006.01.089.PubMed CentralView ArticlePubMedGoogle Scholar
- Kapitonov VV, Jurka J: Rolling-circle transposons in eukaryotes. Proc Natl Acad Sci USA. 2001, 98 (15): 8714-8719. 10.1073/pnas.151269298.PubMed CentralView ArticlePubMedGoogle Scholar
- UCSC Genome Browser.http://genome.ucsc.edu/
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