Group II intron reverse transcriptases (RTs). (A) Group II intron RTs encoded by the L. lactis Ll.LtrB, E. coli EcI5, and Sinorhizobium meliloti RmInt1 introns, which have been converted into targetrons. The Ll.LtrB RT is also referred to as the LtrA protein. (B) Thermostable group II intron RTs from bacterial thermophiles used for biotechnological applications involving cDNA synthesis, such as qRT-PCR, RNA-seq, and miRNA profiling. Group II intron domains are: RT, with conserved RT sequence blocks 1 to 7 found in all RTs (black rectangles) and additional conserved regions RT-0 and RT-2a also found in non-LTR-retrotransposon RTs ; X/thumb, white hatching; DNA binding (D), horizontal black lines; DNA endonuclease (En), black dots.