Mutation of the Rab6 homologue of Saccharomyces cerevisiae, YPT6, inhibits both early Golgi function and ribosome biosynthesis.
A screen was designed to identify temperature-sensitive mutants of Saccharomyces cerevisiae, whose transcription of both ribosomal RNA and ribosomal protein genes is repressed at the nonpermissive temperature. The gene from one such mutant was cloned by complementation. The gene encodes a predicted product that is nearly 65% identical to the human GTPase, Rab6, and is likely to be identical to the yeast gene YPT6. It is essential for growth only at elevated temperatures. The mutant strain is partially defective in the maturation of the vacuolar protein carboxypeptidase Y, as well as in the secretion of invertase, which accumulates as a core-glycosylated form characteristic of the endoplasmic reticulum or the cis-Golgi, suggesting that Ypt6p is involved in an early step of the secretory pathway, earlier than that reported for the mammalian Rab6. The mutant protein, a truncation at codon 64 of 215, has a stronger phenotype than the null allele of YPT6. Four other mutants selected for defective ribosome synthesis at the nonpermissive temperature were also found to have defects in carboxypeptidase Y maturation, giving emphasis to our previous finding that a functional secretory pathway is essential for continued ribosome synthesis. Cloning of extragenic suppressors of the ts allele of YPT6 has revealed two additional proteins that influence the secretory pathway: Ssd1p, a suppressor of many mutations, and Imh1p, which bears some homology to the C-terminal portion of the cytoskeletal proteins integrin and myosin.
Li
B
B
Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Warner
J R
JR
D000595:Amino Acid Sequence; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics*; D003001:Cloning, Molecular; D017931:DNA Primers; D005656:Fungal Proteins / Q000235:genetics*; D019204:GTP-Binding Proteins / Q000235:genetics*; D016153:Genes, Suppressor; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism / Q000502:physiology*; D006358:Hot Temperature; D006801:Humans; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins; D009154:Mutation; D014009:Onychomycosis; D012335:RNA, Ribosomal / Q000096:biosynthesis / Q000235:genetics; D012269:Ribosomal Proteins / Q000096:biosynthesis / Q000235:genetics; D012270:Ribosomes / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic; D020691:rab GTP-Binding Proteins; D018631:ras Proteins / Q000235:genetics*
D002352:Carrier Proteins; D017931:DNA Primers; D005656:Fungal Proteins; D012335:RNA, Ribosomal; C094135:Rab6 protein; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; D019204:GTP-Binding Proteins; D020559:Monomeric GTP-Binding Proteins; C499307:YPT6 protein, S cerevisiae; D020691:rab GTP-Binding Proteins; D018631:ras Proteins