title: An E2 accessory domain increases affinity for the anaphase-promoting complex and ensures E2 competition.
abstract: The anaphase-promoting complex/cyclosome (APC/C) is a member of the RING family of E3 ubiquitin ligases, which promote ubiquitin transfer from an E2 ubiquitin-conjugating enzyme to a substrate. In budding yeast, the APC/C collaborates with two E2s, Ubc4 and Ubc1, to promote the initiation and elongation, respectively, of polyubiquitin chains on the substrate. Ubc4 and Ubc1 are thought to compete for the same site on the APC/C, but it is not clear how their affinities are balanced. Here, we demonstrate that a C-terminal ubiquitin-associated (UBA) domain enhances the affinity of Ubc1 for the APC/C. Deletion of the UBA domain reduced apparent APC/C affinity for Ubc1 and decreased polyubiquitin chain length. Surprisingly, the positive effect of the UBA domain was not due to an interaction with the acceptor ubiquitin attached to the APC/C substrate or the donor ubiquitin attached to Ubc1 itself. Instead, our evidence suggests that the UBA domain binds to a site on the APC/C core, thereby increasing Ubc1 affinity and enhancing its ability to compete with Ubc4. The UBA domain is required for normal Ubc1 function and E2 competition in vivo. Thus, the UBA domain of Ubc1 ensures efficient polyubiquitination of substrate by balancing Ubc1 affinity with that of Ubc4.
authors: From the Departments of Physiology and Biochemistry and Biophysics and Tetrad Graduate Program, University of California, San Francisco, California 94143.
authors: Juliet R
authors: JR
authors: Girard
authors: From the Departments of Physiology and Biochemistry and Biophysics and.
authors: Jeanette L
authors: JL
authors: Tenthorey
authors: From the Departments of Physiology and Biochemistry and Biophysics and Tetrad Graduate Program, University of California, San Francisco, California 94143 david.morgan@ucsf.edu.
authors: David O
authors: DO
authors: Morgan
mesh_terms: D000705:Anaphase; D064173:Anaphase-Promoting Complex-Cyclosome / Q000378:metabolism*; D000818:Animals; D003001:Cloning, Molecular; D025821:Polyubiquitin / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011817:Rabbits; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D025801:Ubiquitin / Q000737:chemistry; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D054875:Ubiquitination
chemical_list: D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; D025821:Polyubiquitin; C066752:UBC1 protein, S cerevisiae; C501306:Ubc4 protein, S cerevisiae; D044763:Ubiquitin-Conjugating Enzymes; D064173:Anaphase-Promoting Complex-Cyclosome; D044767:Ubiquitin-Protein Ligases
keywords: E3 ubiquitin ligase; cell cycle; ubiquitin; ubiquitin-conjugating enzyme (E2 enzyme); yeast