Document Detail

Suppressors of clathrin deficiency: overexpression of ubiquitin rescues lethal strains of clathrin-deficient Saccharomyces cerevisiae.
MedLine Citation:
PMID:  8380227     Owner:  NLM     Status:  MEDLINE    
Clathrin-mediated vesicular transport is important for normal growth of the yeast Saccharomyces cerevisiae. Previously, we identified a genetic locus (SCD1) that influences the ability of clathrin heavy-chain-deficient (Chc-) yeast cells to survive. With the scd1-v allele, Chc- yeast cells are viable but grow poorly; with the scd1-i allele, Chc- cells are inviable. To identify the SCD1 locus and other genes that can rescue chc1 delta scd1-i cells to viability, a multicopy suppressor selection strategy was developed. A strain of scd1-i genotype carrying the clathrin heavy-chain gene under GAL1 control (GAL1:CHC1) was transformed with a YEp24 yeast genomic library, and colonies that could grow on glucose were selected. Plasmids from six distinct genetic loci, none of which encoded CHC1, were recovered. One of the suppressor loci was shown to be UBI4, the polyubiquitin gene. UBI4 rescues only in high copy number and is not allelic to SCD1. The conjugation of ubiquitin to intracellular proteins can mediate their selective degradation. Since UBI4 is required for survival of yeast cells under stress and is induced during starvation, ubiquitin expression in GAL1:CHC1 cells was examined. After a shift to growth on glucose to repress synthesis of clathrin heavy chains, UBI4 mRNA levels were elevated > 10-fold, whereas the quantity of free ubiquitin declined severalfold relative to that of Chc+ cells. In addition, novel higher-molecular-weight ubiquitin conjugates appeared in clathrin-deficient cells. We suggest that higher levels of ubiquitin are required for turnover of mislocalized or improperly processed proteins that accumulate in the absence of clathrin and that ubiquitin may play a general role in turnover of proteins in the secretory or endocytic pathway.
K K Nelson; S K Lemmon
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Molecular and cellular biology     Volume:  13     ISSN:  0270-7306     ISO Abbreviation:  Mol. Cell. Biol.     Publication Date:  1993 Jan 
Date Detail:
Created Date:  1993-01-27     Completed Date:  1993-01-27     Revised Date:  2009-11-18    
Medline Journal Info:
Nlm Unique ID:  8109087     Medline TA:  Mol Cell Biol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  521-32     Citation Subset:  IM    
Department of Molecular Biology and Microbiology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4960.
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MeSH Terms
Clathrin / genetics*
Cloning, Molecular
DNA, Fungal / genetics
Gene Expression
Genes, Fungal
Genes, Lethal
Genes, Suppressor
Genetic Complementation Test
RNA, Fungal / genetics
RNA, Messenger / genetics
Restriction Mapping
Saccharomyces cerevisiae / genetics*
Ubiquitins / physiology*
Grant Support
Reg. No./Substance:
0/Clathrin; 0/DNA, Fungal; 0/RNA, Fungal; 0/RNA, Messenger; 0/Ubiquitins

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