GROUPII INTRONS AND THE ORIGIN OF NUCLEAR PRECURSOR mRNA INTRONS

GroupⅡintrons have attracted considerable attention as mobile genetic elements and possible progenitors of nuclear precursor mRNA introns. GroupⅡintrons can act as mobile factors spreading within a genome or invading new genomes through the mechanism of retrohoming and retrotransposition. The types of groupⅡ introns and comparasion between groupⅡintrons and nuclear pre-mRNA introns are also reviewed. On the origin,the striking similarity between groupⅡand nuclear pre-mRNA splicing mechanisms,together with the mobility of groupⅡintrons, provides the hypothesis that self-splicing groupⅡintrons may be the evolutionary progenitors of eukaryotic nuclear pre-mRNA introns with evindences.