The eukaryotic 20S proteasome is formed by dimerization of two precursor complexes containing the maturation factor Ump1. beta7/Pre4 is the only one of the 14 subunits forming the 20S proteasome that is absent from these precursor complexes in Saccharomyces cerevisiae. Increased expression of Pre4 leads to a reduction in the level of precursor complex indicating that Pre4 incorporation into these complexes is rate-limiting for their dimerization. When we purified these precursor complexes, we observed co-purification of Blm10, a large protein known to attach to the a ring surface of proteasomes. In contrast to single mutants lacking either Blm10 or the C terminal extension of Pre4, a mutant lacking both grew extremely poorly, accumulated very high levels of precursor complexes, and was impaired in beta subunit maturation. The effect of blm10 on proteasome biogenesis is modest apparently because the 19S regulatory particle is capable of substituting for Blm10, as long as precursor complex dimers are stabilized by the Pre4 C terminus. We found that a mutation (sen3/rpn2) affecting the Rpn2 subunit inhibits attachment of the 19S activator to the 20S particle or its precursors. While the sen3 mutation alone had no apparent effect on precursor complex dimerization and active site maturation, the sen3 blm10 double mutant was impaired in these processes. Together these data demonstrate that Blm10 and the 19S activator have a partially redundant function in stabilizing nascent 20S proteasomes and in promoting their activation.
|Evidence ID||Analyze ID||Interactor||Interactor Systematic Name||Interactor||Interactor Systematic Name||Type||Assay||Annotation||Action||Modification||Phenotype||Source||Reference||Note|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Gene Ontology Term||Gene Ontology Term ID||Qualifier||Aspect||Method||Evidence||Source||Assigned On||Reference||Annotation Extension|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Phenotype||Experiment Type||Experiment Type Category||Mutant Information||Strain Background||Chemical||Details||Reference|
|Evidence ID||Analyze ID||Regulator||Regulator Systematic Name||Target||Target Systematic Name||Experiment||Conditions||Strain||Source||Reference|