title: Genetic interactions of hypomorphic mutations in the m7G cap-binding pocket of yeast nuclear cap binding complex: an essential role for Cbc2 in meiosis via splicing of MER3 pre-mRNA.
abstract: Nuclear cap binding protein complex (CBC) is a heterodimer of a small subunit (Cbc2 in yeast) that binds the m(7)G cap and a large subunit (Sto1 in yeast) that interacts with karyopherins. In order to probe the role of cap recognition in yeast CBC function, we introduced alanine mutations (Y24A, F91A, D120A, D122A, R129A, and R133A) and N-terminal deletions (NΔ21 and NΔ42) in the cap-binding pocket of Cbc2. These lesions had no effect on vegetative growth, but they ameliorated the cold-sensitivity of tgs1Δ cells that lack trimethylguanosine caps (a phenotype attributed to ectopic association of CBC with the m(7)G cap of the normally TMG-capped U1 snRNA), thereby attesting to their impact on cap binding in vivo. Further studies of the Cbc2-Y24A variant revealed synthetic lethality or sickness with null mutations of proteins involved in early steps of spliceosome assembly (Nam8, Mud1, Swt21, Mud2, Ist3, and Brr1) and with otherwise benign mutations of Msl5, the essential branchpoint binding protein. Whereas the effects of weakening CBC-cap interactions are buffered by other actors in the splicing pathway during mitotic growth, the NΔ42 allele causes a severe impediment to yeast sporulation and meiosis. RNA analysis revealed a selective defect in the splicing of MER3 and SAE3 transcripts in cbc2-NΔ42 diploids during attempted sporulation. An intronless MER3 cDNA fully restored sporulation and spore viability in the cbc2-NΔ42 strain, signifying that MER3 splicing is a limiting transaction. These studies reveal a new level of splicing control during meiosis that is governed by nuclear CBC.
authors.affiliation: Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10065, USA.
authors.forename: Zhicheng R
authors.initials: ZR
authors.lastname: Qiu
authors.forename: Lidia
authors.initials: L
authors.lastname: Chico
authors.forename: Jonathan
authors.initials: J
authors.lastname: Chang
authors.forename: Stewart
authors.initials: S
authors.lastname: Shuman
authors.forename: Beate
authors.initials: B
authors.lastname: Schwer
mesh_terms: D020816:Amino Acid Motifs; D019943:Amino Acid Substitution; D001483:Base Sequence; D001665:Binding Sites; D004265:DNA Helicases / Q000235:genetics* / Q000378:metabolism; D004843:Epistasis, Genetic; D055786:Gene Knockout Techniques; D007438:Introns; D008540:Meiosis; D008780:Methyltransferases / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D039502:Nuclear Cap-Binding Protein Complex / Q000235:genetics* / Q000502:physiology; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D012322:RNA Precursors / Q000235:genetics / Q000378:metabolism; D012326:RNA Splicing; D000072260:RNA Splicing Factors; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D045522:Recombinases / Q000235:genetics / Q000378:metabolism; D012261:Ribonucleoproteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D000072668:Splicing Factor U2AF; D013172:Spores, Fungal / Q000235:genetics / Q000254:growth & development / Q000502:physiology
chemical_list: C100383:CBC2 protein, S cerevisiae; C409040:MSL5 protein, S cerevisiae; C089980:MUD2 protein, S cerevisiae; D039502:Nuclear Cap-Binding Protein Complex; D009687:Nuclear Proteins; C528119:Pch2 protein, S cerevisiae; D012322:RNA Precursors; D000072260:RNA Splicing Factors; D012331:RNA, Fungal; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D045522:Recombinases; D012261:Ribonucleoproteins; C107851:SAE3 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D000072668:Splicing Factor U2AF; D008780:Methyltransferases; C456271:trimethylguanosine synthase; C455499:HFM1 protein, S cerevisiae; D004265:DNA Helicases