title: GSP1 and GSP2, genetic suppressors of the prp20-1 mutant in Saccharomyces cerevisiae: GTP-binding proteins involved in the maintenance of nuclear organization.
abstract: The temperature-sensitive mutation prp20-1 of Saccharomyces cerevisiae exhibits a pleiotropic phenotype associated with a general failure to maintain a proper organization of the nucleus. Its mammalian homolog, RCC1, is not only reported to be involved in the negative control of chromosome condensation but is also believed to assist in the coupling of DNA replication to the entry into mitosis. Recent studies on Xenopus RCC1 have strongly suggested a further role for this protein in the formation or maintenance of the DNA replication machinery. To elucidate the nature of the various components required for this PRP20 control pathway in S. cerevisiae, we undertook a search for multicopy suppressors of a prp20 thermosensitive mutant. Two genes, GSP1 and GSP2, were identified that encode almost identical polypeptides of 219 and 220 amino acids. Sequence analyses of these proteins show them to contain the ras consensus domains involved in GTP binding and metabolism. The levels of the GSP1 transcript are about 10-fold those of GSP2. As for S. cerevisiae RAS2, GSP2 expression exhibits carbon source dependency, while GSP1 expression does not. GSP1 is an essential gene, and GSP2 is not required for cell viability. We show that GSP1p is nuclear, that it can bind GTP in an in vitro assay, and finally, that a mutation in GSP1p which activates small ras-like proteins by increasing the stability of the GTP-bound form causes a dominant lethal phenotype. We believe that these two gene products may serve in regulating the activities of the multicomponent PRP20 complex.
authors.affiliation: Department of Biology, McGill University, Montréal, Québec, Canada.
authors.forename: P
authors.initials: P
authors.lastname: Belhumeur
authors.forename: A
authors.initials: A
authors.lastname: Lee
authors.forename: R
authors.initials: R
authors.lastname: Tam
authors.forename: T
authors.initials: T
authors.lastname: DiPaolo
authors.forename: N
authors.initials: N
authors.lastname: Fortin
authors.forename: M W
authors.initials: MW
authors.lastname: Clark
mesh_terms: D001483:Base Sequence; D002466:Cell Nucleolus / Q000648:ultrastructure*; D003001:Cloning, Molecular; D005656:Fungal Proteins / Q000235:genetics; D019204:GTP-Binding Proteins / Q000235:genetics*; D015870:Gene Expression; D005799:Genes, Dominant; D005800:Genes, Fungal; D005804:Genes, Lethal; D016153:Genes, Suppressor; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins; D009687:Nuclear Proteins / Q000235:genetics*; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D012331:RNA, Fungal / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment
chemical_list: D005656:Fungal Proteins; C080324:GSP1 protein, S cerevisiae; D009687:Nuclear Proteins; D009838:Oligodeoxyribonucleotides; D012331:RNA, Fungal; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D019204:GTP-Binding Proteins; C080325:GSP2 protein, S cerevisiae; D020559:Monomeric GTP-Binding Proteins