Son1p is a component of the 26S proteasome of the yeastSaccharomyces cerevisiae

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Abstract
A son1 mutant was isolated as a mutant showing synthetic lethality with nin1‐1 which is defective in the p31 component of the regulatory subunit of the yeast 26S proteasome. son1Δ showed a synthetic effect with sen3Δ and sun1Δ, both components of the 26S proteasome, and with cdc28‐1N. The 26S proteasome was partially purified from the wild type yeast. The FPLC fractions were analyzed by Western blotting using anti‐Son1p antibody and antibodies against some authentic subunits of the 26S proteasome, and we found that Son1p co‐migrated with components of the 26S proteasome. The 26S proteasome containing fraction was immunoprecipitated with anti‐Son1p antibody. The resultant precipitate contained Nin1p, Sun1p, TBP1, and the 20S proteasome. Combining genetic and biochemical results together, we concluded that Son1p is a component of the yeast 26S proteasome.