The ins and outs of group II introns

Group II introns have attracted considerable attention as ribozymes, mobile genetic elements and possible progenitors of nuclear spliceosomal introns. Major advances in understanding their catalytic structure and dispersal st rategies have recently come from several model mitochondrial and bacterial self-splicing introns. In Nature, this family of introns shows wide variati on in both features and behaviour, and this review includes a focus on the diversity of evolutionary pathways taken.