title: Lysine 63-linked polyubiquitin chain may serve as a targeting signal for the 26S proteasome.
abstract: Recruitment of substrates to the 26S proteasome usually requires covalent attachment of the Lys48-linked polyubiquitin chain. In contrast, modifications with the Lys63-linked polyubiquitin chain and/or monomeric ubiquitin are generally thought to function in proteasome-independent cellular processes. Nevertheless, the ubiquitin chain-type specificity for the proteasomal targeting is still poorly understood, especially in vivo. Using mass spectrometry, we found that Rsp5, a ubiquitin-ligase in budding yeast, catalyzes the formation of Lys63-linked ubiquitin chains in vitro. Interestingly, the 26S proteasome degraded well the Lys63-linked ubiquitinated substrate in vitro. To examine whether Lys63-linked ubiquitination serves in degradation in vivo, we investigated the ubiquitination of Mga2-p120, a substrate of Rsp5. The polyubiquitinated p120 contained relatively high levels of Lys63-linkages, and the Lys63-linked chains were sufficient for the proteasome-binding and subsequent p120-processing. In addition, Lys63-linked chains as well as Lys48-linked chains were detected in the 26S proteasome-bound polyubiquitinated proteins. These results raise the possibility that Lys63-linked ubiquitin chain also serves as a targeting signal for the 26S proteaseome in vivo.
authors.affiliation: Laboratory of Frontier Science, Core Technology and Research Center, Tokyo Metropolitan Institute of Medical Science, Bunkyo-ku, Tokyo, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Saeki
authors.forename: Tai
authors.initials: T
authors.lastname: Kudo
authors.forename: Takayuki
authors.initials: T
authors.lastname: Sone
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Kikuchi
authors.forename: Hideyoshi
authors.initials: H
authors.lastname: Yokosawa
authors.forename: Akio
authors.initials: A
authors.lastname: Toh-e
authors.forename: Keiji
authors.initials: K
authors.lastname: Tanaka
mesh_terms: D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D008239:Lysine / Q000737:chemistry*; D013058:Mass Spectrometry / Q000379:methods; D008565:Membrane Proteins; D008954:Models, Biological; D010957:Plasmids / Q000378:metabolism; D025821:Polyubiquitin / Q000737:chemistry*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors; D025801:Ubiquitin / Q000737:chemistry; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism*; D020729:p120 GTPase Activating Protein / Q000378:metabolism
chemical_list: D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D056827:Endosomal Sorting Complexes Required for Transport; C542266:MGA2 protein, S cerevisiae; D008565:Membrane Proteins; C086926:SIC1 protein, S cerevisiae; C087570:SPT23 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D025801:Ubiquitin; D020729:p120 GTPase Activating Protein; D025821:Polyubiquitin; D043743:Ubiquitin-Protein Ligase Complexes; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; C469287:RSP5 protein, S cerevisiae; D008239:Lysine