Abstract
The selective recognition of ubiquitin conjugates by proteasomes is a key step in protein degradation. The receptors that mediate this step have yet to be clearly defined although specific candidates exist. Here we show that the proteasome directly recognizes ubiquitin chains through a specific subunit, Rpn10, and also recognizes chains indirectly through Rad23, a reversibly bound proteasome cofactor. Both binding events can be observed in purified biochemical systems. A block substitution in the chain-binding ubiquitin interacting motif of RPN10 when combined with a null mutation in RAD23 results in a synthetic defect in protein degradation consistent with the view that the direct and indirect recognition modes function to some extent redundantly in vivo. Rad23 and the deubiquitinating enzyme Ubp6 both bind proteasome subunit Rpn1 through N-terminal ubiquitin-like domains. Surprisingly, Rad23 and Ubp6 do not compete with each other for proteasome binding. Thus, Rpn1 may act as a scaffold to assemble on the proteasome multiple proteins that act to either bind or hydrolyze multiubiquitin chains.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Motifs
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Binding, Competitive
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Canavanine / pharmacology
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Carrier Proteins / chemistry
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Carrier Proteins / genetics
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Carrier Proteins / metabolism*
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Cysteine Endopeptidases / chemistry
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Cysteine Endopeptidases / genetics
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Cysteine Endopeptidases / metabolism*
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / metabolism*
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Endopeptidases / metabolism
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Fungal Proteins / genetics
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Fungal Proteins / metabolism*
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Multienzyme Complexes / chemistry
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Multienzyme Complexes / genetics
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Multienzyme Complexes / metabolism*
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Mutation
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Proteasome Endopeptidase Complex
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Protein Binding
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Protein Structure, Tertiary
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Protein Subunits
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Recombinant Proteins / chemistry
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Recombinant Proteins / genetics
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Recombinant Proteins / metabolism
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Saccharomyces cerevisiae / chemistry
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Saccharomyces cerevisiae / genetics
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Saccharomyces cerevisiae / metabolism
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Saccharomyces cerevisiae Proteins / metabolism
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Ubiquitins / chemistry
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Ubiquitins / metabolism*
Substances
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Carrier Proteins
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DNA-Binding Proteins
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Fungal Proteins
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Multienzyme Complexes
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Protein Subunits
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RAD23 protein, S cerevisiae
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RPN10 protein, S cerevisiae
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Recombinant Proteins
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Saccharomyces cerevisiae Proteins
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Ubiquitins
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Canavanine
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Endopeptidases
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Cysteine Endopeptidases
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Proteasome Endopeptidase Complex
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UBP6 protein, S cerevisiae