A reverse transcriptase/maturase promotes splicing by binding at its own coding segment in a group II intron RNA

Group II introns encode reverse transcriptases that promote RNA splicing (maturase activity) and then with the excised intron form a DNA endonuclease that mediates intron mobility by target DNA-primed reverse transcription (TPRT). Here, we show that the primary binding site for the maturase (LtrA) encoded by the Lactococcus lactis Ll.LtrB intron is within a region of intron domain IV that includes the start codon of the LtrA ORF. This binding is enhanced by other elements, particularly domain I and the EBS/IBS interactions, and helps position LtrA to initiate cDNA synthesis in the 3' exon as occurs during TPRT. Our results suggest how the maturase functions in RNA splicing and support the hypothesis that the reverse transcriptase coding region was derived from an independent genetic element that was inserted into a preexisting group II intron.