title: Context of multiubiquitin chain attachment influences the rate of Sic1 degradation.
abstract: The ubiquitin-dependent targeting of proteins to the proteasome is an essential mechanism for regulating eukaryotic protein stability. Here we define the minimal signal for the degradation of the S phase CDK inhibitor Sic1. Of 20 lysines scattered throughout Sic1, 6 N-terminal lysines serve as major ubiquitination sites. Sic1 lacking these lysines (K0N) is stable in vivo, but readdition of any one restores turnover. Nevertheless, ubiquitin chains attached at different N-terminal lysines specify degradation in vitro at markedly different rates. Moreover, although K0N can be ubiquitinated by SCF(Cdc4)/Cdc34 in vitro in the absence (but not in the presence) of S-CDK, it is degraded slowly. Our results reveal that a single multiubiquitin chain can sustain a physiological turnover rate, but that chain position plays an unexpectedly significant role in the rate of proteasomal proteolysis.
authors.affiliation: Howard Hughes Medical Institute, Division of Biology 156-29, California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, USA.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Petroski
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Deshaies
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D004791:Enzyme Inhibitors / Q000378:metabolism*; D008239:Lysine / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D013379:Substrate Specificity; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D004791:Enzyme Inhibitors; D011993:Recombinant Fusion Proteins; C086926:SIC1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; D008239:Lysine