title: Investigating the importance of proteasome-interaction for Rad23 function.
abstract: Rad23 contributes to diverse cellular functions that include DNA repair, stress response and growth control. An amino-terminal ubiquitin-like (UbL) domain in Rad23 interacts with catalytically active proteasomes and internal sequences bind multi-ubiquitinated proteins. Rad23 regulates the assembly of substrate-linked multi-ubiquitin chains, promotes efficient degradation of model substrates, and plays an overlapping role with the proteasome subunit, Rpn10. These and other results led to the hypothesis that Rad23 translocates proteolytic substrates to the proteasome to promote degradation. It was previously shown that the UbL domain in Rad23 could be functionally replaced by ubiquitin. However, monomeric ubiquitin does not bind the proteasome efficiently, and we therefore investigated whether proteasome interaction was required for all Rad23 functions. We report here that the ubiquitin moiety in Ub-rad23 is ubiquitinated in vivo and could provide an alternate mechanism for binding the proteasome. These results suggest that the localization of Rad23 to the proteasome, either by its UbL domain, or following ubiquitination of an amino-terminal ubiquitin moiety (Ub-rad23), is necessary for full activity.
authors.affiliation: Department of Biochemistry, Room 628, Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854, USA.
authors.forename: David
authors.initials: D
authors.lastname: Lambertson
authors.forename: Li
authors.initials: L
authors.lastname: Chen
authors.forename: Kiran
authors.initials: K
authors.lastname: Madura
mesh_terms: D002352:Carrier Proteins; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism*; D009154:Mutation; D046988:Proteasome Endopeptidase Complex; D012097:Repressor Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D009097:Multienzyme Complexes; C490846:RAD23 protein, S cerevisiae; C122019:RPN10 protein, S cerevisiae; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex