title: U4 small nuclear RNA can function in both the major and minor spliceosomes.
abstract: U4 small nuclear RNA (snRNA) and U6 snRNA form a base-paired di-snRNP complex that is essential for pre-mRNA splicing of the major class of metazoan nuclear introns. The functionally analogous but highly diverged U4atac and U6atac snRNAs form a similar complex that is involved in splicing of the minor class of introns. Previous results with mutants of U6atac in which a substructure was replaced by the analogous structure from U6 snRNA suggested that wild-type U4 snRNA might be able to interact productively with the mutant U6atac snRNA. Here we show that a mutant U4 snRNA designed to base pair with a mutant U6atac snRNA can activate U12-dependent splicing when coexpressed in an in vivo genetic suppression assay. This genetic interaction could also be demonstrated in an in vitro crosslinking assay. These results show that a U4/U6atac di-snRNP can correctly splice a U12-dependent intron and suggest that the specificity for spliceosome type resides in the U6 and U6atac small nuclear ribonucleoproteins. Further experiments suggest that expression of a mutant U4 snRNA that can bind to wild-type U6atac snRNA alters the specificity of some splice sites, providing an evolutionary rationale for maintaining two U4-like snRNAs.
authors.affiliation: Department of Molecular Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH 44195, USA.
authors.forename: Girish C
authors.initials: GC
authors.lastname: Shukla
authors.forename: Richard A
authors.initials: RA
authors.lastname: Padgett
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D006801:Humans; D066298:In Vitro Techniques; D007438:Introns; D008958:Models, Molecular; D009154:Mutation; D009690:Nucleic Acid Conformation; D012313:RNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012326:RNA Splicing; D018749:RNA, Plant / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012342:RNA, Small Nuclear / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017381:Spliceosomes / Q000378:metabolism*
chemical_list: D018749:RNA, Plant; D012342:RNA, Small Nuclear; C039919:RNA, recombinant; C405482:U4 small nuclear RNA; C405486:U6 small nuclear RNA; D012313:RNA