Figure 1.
Structure of the IIA Ll.LtrB group II intron and its intron-encoded protein.
A. RNA secondary structure. The intron is indicated by thin black lines and exons by thick black lines. Sequence elements involved in long-range Watson-Crick and non-Watson-Crick interactions are indicated by gray shading and boxes, respectively. The ORF is encoded within a “loop” of DIV (dashed lines).
B. The group II IEP has four domains: reverse transcriptase (RT) with conserved sequence blocks 0-7; X/thumb domain; D, DNA-binding; and En, DNA endonuclease.