Bacterial group II introns and their association with mobile genetic elements

Group II introns are an abundant class of self-splicing RNAs, found primarily in the organelles of plants and lower eukaryotes and in bacteria. The first bacterial group II intron identified to be functional for splicing in vivo was the Ll.ltrB intron of Lactococcus lactis. It has served as an excellent model for the study of group II intron structure and function. Taking advantage of the tools of bacterial genetics and biochemical methodologies, details of Ll.ltrB splicing and homing reactions have been elucidated and are similar to those of fungal group II introns. This review provides a summary of these results. Of particular interest is the potential use of Ll.ltrB as an agent for targeted gene disruption. In addition, the development of a genetic system to analyze Ll.ltrB splicing promises to provide new insight into group II intron structure and function. Identification and analysis of group II introns in other bacterial species is a continuing process, and a discussion of published reports on these introns is provided here. Limited functional data is available for most of these introns, but sequence analysis points out several common themes, most notably that bacterial group II introns are almost always carried on mobile genetic elements.