Figure 3. Elevated peptidase activity of proteasome holocomplexes in ubr2Δ and mub1Δ cells.

(A) Elevated cellular proteasomal peptidase activity in ubr2Δ and mub1Δ strains. The three distinct proteasomal peptidase activities of the strains indicated were tested with 50 µg of total protein in the presence of 100 µM of the fluorogenic substrates Suc-LLVY-AMC (chymotrypsin-like activity), Boc-RLR-AMC (trypsin-like activity) and Ac-nLPnLD-AMC (caspase activity). The reactions were recorded in the absence or presence of 50 µg/ml of the proteasome inhibitor MG132 (Figure S2) to demonstrate specificity of the reactions. The mean +/− SEM of three technical replicates is presented. (B) Growth is unaffected in cells with increased proteasome abundance. Growth curves of WT, rpn4Δ, ubr2Δ, mub1Δ, rpn4Δ ubr2Δ and rpn4Δ mub1Δ strains were recorded in a Bioscreen C MB machine in YPD at 30°C. Doubling times are listed in Figure S3.