Increased degradation of oxidized proteins in yeast defective in 26S proteasome assembly

An Rpn9-disrupted yeast strain, Deltarpn9, whose growth is temperature sensitive with defective assembly of the 26 S proteasome complex, was studied. This mutant yeast was more resistant to hydrogen peroxide treatment and able to degrade carbonylated proteins more efficiently than wild type. Nondenaturing gel electrophoresis followed by activity staining revealed that Deltarpn9 yeast cells had a higher activity of 20 S proteasome than wild type and that in both Deltarpn9 and wild-type cells treated with hydrogen peroxide, 20 S proteasome activity was increased with a concomitant decrease in 26 S proteasome activity. Protein multiubiquitination was not observed in the hydrogen peroxide-treated cells. Taken together, these results suggest that the 20 S proteasome degrades oxidized proteins without ubiquitination of target proteins. (C) 2002 Elsevier Science (USA). All rights reserved.