genetic screen for Saccharomyces cerevisiae mutants affecting proteasome function, using a ubiquitin-independent substrate

The great majority of proteasome substrates are marked for degradation by the attachment of polyubiquitin chains. Ornithine decarboxylase is degraded by the proteasome in the absence of this modification. We previously showed that this mechanism of degradation was conserved in eukaryotic cells. Here...

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Published in:	Yeast (Chichester, England) Vol. 25; no. 3; pp. 199 - 217
Main Authors:	Hoyt, Martin A, McDonough, Stephen, Pimpl, Stephan A, Scheel, Hartmut, Hofmann, Kay, Coffino, Philip
Format:	Journal Article
Language:	English
Published:	Chichester, UK John Wiley & Sons, Ltd 01-03-2008
Subjects:	Amino Acid Sequence Animals Mice Molecular Chaperones - isolation & purification Molecular Sequence Data ornithine decarboxylase Ornithine Decarboxylase - metabolism Poc3 Poc4 proteasome Proteasome Endopeptidase Complex - physiology Saccharomyces cerevisiae Saccharomyces cerevisiae - genetics Saccharomyces cerevisiae - physiology Saccharomyces cerevisiae Proteins - genetics Saccharomyces cerevisiae Proteins - isolation & purification Saccharomyces cerevisiae Proteins - metabolism Sequence Alignment Sequence Deletion Substrate Specificity ubiquitin Ubiquitin - metabolism
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Summary:	The great majority of proteasome substrates are marked for degradation by the attachment of polyubiquitin chains. Ornithine decarboxylase is degraded by the proteasome in the absence of this modification. We previously showed that this mechanism of degradation was conserved in eukaryotic cells. Here we use a reporter destabilized by mouse ornithine decarboxylase to screen non-essential Saccharomyces cerevisiae deletion mutants. We identified novel mutants that affect both ubiquitin-dependent and -independent proteasome degradation pathways. YLR021W (IRC25/POC3) and YPL144W (POC4) encode interacting proteins that function in proteasome assembly, with putative homologues widespread among eukaryotes. Several additional mutants suffered from defects in proteasome-mediated proteolysis. These included mutants in the urmylation pathway of protein modification (but not the Urm1 modifier itself) and the Reg1 regulatory subunit of protein phosphatase 1. Finally, we noted increased rates of ornithine decarboxylase turnover in an rpn10Δ mutant in which the degradation of certain ubiquitinated substrates is impaired. Together, these results highlight the utility of a ubiquitin-independent degron in uncovering novel factors affecting general and substrate-specific proteasome function. Copyright © 2008 John Wiley & Sons, Ltd.
Bibliography:	http://dx.doi.org/10.1002/yea.1579 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0749-503X 1097-0061
DOI:	10.1002/yea.1579