Splicing of a group II intron involved in the conjugative transfer of pRS01 in lactococci

Analysis of a region involved in the conjugative transfer of the lactococcal conjugative element pRS01 has revealed a bacterial group II intron. Splicing of this lactococcal intron (designated L1.ltrB) in vivo resulted in the ligation of two exon messages (ItrBE1 and ItrBE2) which encoded a putative conjugative relaxase essential for the transfer of pRSO1. Like many group II introns, the L1.ltrB intron possessed an open reading frame (ItrA) with homolog to reverse transcriptases. Remarkably, sequence analysis of ltrA suggested a greater similarity to open reading frames encoded by eukaryotic mitochondrial group II introns than to those identified to date from other bacteria, Several insertional mutations within ItrA resulted in plasmids exhibiting a conjugative transfer-deficient phenotype. These results provide the first direct evidence for splicing of a prokaryotic group II intron in vivo and suggest that conjugative transfer is a mechanism for group II intron dissemination in bacteria.