title: A subset of Mer1p-dependent introns requires Bud13p for splicing activation and nuclear retention.
abstract: In the yeast Saccharomyces cerevisiae, Mer1p is expressed only during meiosis, and its expression is linked to the splicing of at least three mRNAs: MER2, MER3, and AMA1. Previous evidence suggests that Mer1p activates splicing by directly recruiting snRNPs or stabilizing intermediate splicing complexes formed on pre-mRNA that contains an intronic Mer1p enhancer element. However, some splicing factors, especially accessory/non-snRNP factors, have critical roles in retaining unspliced pre-mRNAs in the nucleus. We tested if Mer1p may indirectly regulate splicing by preventing the export of pre-mRNAs to the cytoplasm and also demonstrated that a second subunit of the Retention and Splicing (RES) complex, Bud13p, has transcript-specific effects on Mer1p-activated splicing. The results indicated that Mer1p can retain unspliced pre-mRNA in the nucleus; however, nuclear retention could not be uncoupled from splicing activation. In the absence of Mer1p, the AMA1 pre-mRNA is exported to the cytoplasm, translated, but not subjected to nonsense-mediated decay (NMD) despite a premature stop codon in the intron. These data imply that Mer1p can retain pre-mRNAs in the nucleus only by facilitating their interaction with the spliceosome and that two subunits of the RES complex modulate Mer1p function on two of the three Mer1p-dependent introns. The results also support models for cytoplasmic degradation of unspliced pre-mRNAs that fail to assemble into spliceosomes in yeast.
authors.affiliation: Department of Biology, University of Missouri-St. Louis, MO 63121, USA.
authors.forename: Frederick W
authors.initials: FW
authors.lastname: Scherrer
authors.forename: Marc
authors.initials: M
authors.lastname: Spingola
mesh_terms: D002467:Cell Nucleus / Q000235:genetics; D007438:Introns / Q000235:genetics*; D008540:Meiosis; D012322:RNA Precursors / Q000235:genetics; D012326:RNA Splicing / Q000235:genetics; D012331:RNA, Fungal / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics*; D016601:RNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism*
chemical_list: C092601:MER1 protein, S cerevisiae; D012322:RNA Precursors; D012331:RNA, Fungal; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins