SPLICING OF A GROUP-II INTRON IN A FUNCTIONAL TRANSFER GENE OF LACTOCOCCUS-LACTIS

A chromosomally located sex factor that controls conjugation in Lactoc occus lactis 712 has been cloned and sequenced, leading to the discove ry of an open reading frame with homology to the maturases of group II self-splicing introns. Reverse transcriptase polymerase chain reactio n amplification was used to demonstrate that the intron was spliced ou t of mRNA in vivo, and sequence analysis revealed the site of splicing . The intron was inserted within a sex-factor gene which encodes a pro tein with homology to proteins involved in rolling-circle DNA replicat ion. Gene-disruption experiments were used to demonstrate that this mo bA gene was essential for sex-factor transfer and this suggests that i ntron splicing is a necessary part of the conjugation process. The seq uence of the intron was modelled to produce a secondary structure that exhibited several features characteristic of the IIA subgroup. Here w e report the characterization of a new group II intron in the Gram-pos itive bacterium L. lactis and demonstrate for the first time in bacter ia both splicing in vivo and an active role for the gene carrying the intron.