title: An early evolutionary origin for the minor spliceosome.
abstract: The minor spliceosome is a ribonucleoprotein complex that catalyses the removal of an atypical class of spliceosomal introns (U12-type) from eukaryotic messenger RNAs. It was first identified and characterized in animals, where it was found to contain several unique RNA constituents that share structural similarity with and seem to be functionally analogous to the small nuclear RNAs (snRNAs) contained in the major spliceosome. Subsequently, minor spliceosomal components and U12-type introns have been found in plants but not in fungi. Unlike that of the major spliceosome, which arose early in the eukaryotic lineage, the evolutionary history of the minor spliceosome is unclear because there is evidence of it in so few organisms. Here we report the identification of homologues of minor-spliceosome-specific proteins and snRNAs, and U12-type introns, in distantly related eukaryotic microbes (protists) and in a fungus (Rhizopus oryzae). Cumulatively, our results indicate that the minor spliceosome had an early origin: several of its characteristic constituents are present in representative organisms from all eukaryotic supergroups for which there is any substantial genome sequence information. In addition, our results reveal marked evolutionary conservation of functionally important sequence elements contained within U12-type introns and snRNAs.
authors.affiliation: Department of Biochemistry and Molecular Biology, Dalhousie University, 5850 College Street, Halifax, Nova Scotia B3H 1X5, Canada.
authors.forename: Anthony G
authors.initials: AG
authors.lastname: Russell
authors.forename: J Michael
authors.initials: JM
authors.lastname: Charette
authors.forename: David F
authors.initials: DF
authors.lastname: Spencer
authors.forename: Michael W
authors.initials: MW
authors.lastname: Gray
mesh_terms: D048248:Acanthamoeba castellanii / Q000737:chemistry / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D005057:Eukaryotic Cells / Q000378:metabolism; D019143:Evolution, Molecular; D020224:Expressed Sequence Tags; D006801:Humans; D007438:Introns / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D012326:RNA Splicing; D012342:RNA, Small Nuclear / Q000235:genetics / Q000378:metabolism; D012233:Rhizopus / Q000737:chemistry / Q000235:genetics*; D017381:Spliceosomes / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism
chemical_list: D012342:RNA, Small Nuclear