Splicing of a group II intron in a functional transfer gene of Lactococcus lactis.

A chromosomally located sex factor that controls conjugation in Lactococcus lactis 712 has been cloned and sequenced, leading to the discovery of an open reading frame with homology to the maturases of group II self-splicing introns. Reverse transcriptase polymerase chain reaction amplification was used to demonstrate that the intron was spliced out of mRNA in vivo, and sequence analysis revealed the site of splicing. The intron was inserted within a sex-factor gene which encodes a protein with homology to proteins involved in rolling-circle DNA replication. Gene-disruption experiments were used to demonstrate that this mobA gene was essential for sex-factor transfer and this suggests that intron splicing is a necessary part of the conjugation process. The sequence of the intron was modelled to produce a secondary structure that exhibited several features characteristic of the IIA subgroup. Here we report the characterization of a new group II intron in the Gram-positive bacterium L. lactis and demonstrate for the first time in bacteria both splicing in vivo and an active role for the gene carrying the intron.