Figure 1

Group II intron RNA structure and splicing mechanism. (A) Group II intron RNA secondary structure. The example shown is the Lactococcus lactis Ll.LtrB group IIA intron. Intron RNA domains are different colors, and the 5’ and 3’ exons (E1 and E2, respectively) are thicker dark and light blue lines, respectively. The large ‘loop’ region of DIV, which encodes the group II intron RT, is shown as a dashed line and not drawn to scale. (B) Crystal structure of the Oceanobacillus iheyensis group IIC intron. The ribbon diagram of the intron’s structure was generated from Protein Data Bank file 3IGI [20] (http://www.pdb.org) with PyMol. Group II intron RNA domains are colored as in panel A. (C) Group II intron RNA splicing and reverse splicing. Double-stranded DNA is indicated by double lines and RNA as a single line. E1 and E2 are shown in dark and light blue, respectively; the intron and intron RNA are shown in red; and the intron-encoded RT is shown in green.