title: An essential role for trimethylguanosine RNA caps in Saccharomyces cerevisiae meiosis and their requirement for splicing of SAE3 and PCH2 meiotic pre-mRNAs.
abstract: Tgs1 is the enzyme that converts m(7)G RNA caps to the 2,2,7-trimethylguanosine (TMG) caps characteristic of spliceosomal snRNAs. Fungi grow vegetatively without TMG caps, thereby raising the question of what cellular transactions, if any, are TMG cap-dependent. Here, we report that Saccharomyces cerevisiae Tgs1 methyltransferase activity is essential for meiosis. tgs1Δ cells are specifically defective in splicing PCH2 and SAE3 meiotic pre-mRNAs. The TMG requirement for SAE3 splicing is alleviated by two intron mutations: a UAUUAAC to UACUAAC change that restores a consensus branchpoint and disruption of a stem-loop encompassing the branchpoint. The TMG requirement for PCH2 splicing is alleviated by a CACUAAC to UACUAAC change restoring a consensus branchpoint and by shortening the PCH2 5' exon. Placing the SAE3 and PCH2 introns within a HIS3 reporter confers Tgs1-dependent histidine prototrophy, signifying that the respective introns are portable determinants of TMG-dependent gene expression. Analysis of in vitro splicing in extracts of TGS1 versus tgs1Δ cells showed that SAE3 intron removal was enfeebled without TMG caps, whereas splicing of ACT1 was unaffected. Our findings illuminate a new mode of tunable splicing, a reliance on TMG caps for an essential developmental RNA transaction, and three genetically distinct meiotic splicing regulons in budding yeast.
authors.affiliation: Molecular Biology Program, Sloan-Kettering Institute and Department of Microbiology and Immunology, Weill Cornell Medical College, New York, NY 10065 USA.
authors.forename: Zhicheng R
authors.initials: ZR
authors.lastname: Qiu
authors.forename: Stewart
authors.initials: S
authors.lastname: Shuman
authors.forename: Beate
authors.initials: B
authors.lastname: Schwer
mesh_terms: D004720:Endonucleases / Q000235:genetics* / Q000378:metabolism; D005091:Exons; D017353:Gene Deletion; D006151:Guanosine / Q000031:analogs & derivatives / Q000378:metabolism; D007438:Introns; D008540:Meiosis / Q000235:genetics; D008780:Methyltransferases / Q000235:genetics / Q000502:physiology*; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D009690:Nucleic Acid Conformation; D012322:RNA Precursors / Q000378:metabolism; D012326:RNA Splicing; D012333:RNA, Messenger / Q000737:chemistry / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D013172:Spores, Fungal / Q000201:enzymology
chemical_list: C092601:MER1 protein, S cerevisiae; D009687:Nuclear Proteins; C528119:Pch2 protein, S cerevisiae; D012322:RNA Precursors; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; C107849:SAE2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D006151:Guanosine; C017778:N(2),N(2),7-trimethylguanosine; D008780:Methyltransferases; C456271:trimethylguanosine synthase; D004720:Endonucleases