FIG. 1.

MG132 increases the synthesis of hsps in yeast cells. ise1 cells were incubated during growth at 30°C with either 50 μM MG132 (dissolved in DMSO) or 0.1% DMSO (control). (A) The rates of synthesis of several hsps (hsp104, hsp70, Ydj1p, and Sis1p) were then measured by pulse-labeling cells with 200 μCi of [³⁵S]methionine for 30 min at different times. Shown are the times at the end of the 30-min pulse (1, 2, or 3 h after MG132 was added). After cell lysis, immunoprecipitation with antibodies against these hsps was performed with equal amounts of radioactive proteins in control or MG132-treated cells. (B) Relative induction rates of these four hsps based on data in panel A. Data shown are the mean values ± SD from three independent experiments. (C) To show that these effects of MG132 were due to enhanced synthesis of hsps, the ise1 cell were incubated with either 50 μM MG132 or 0.1% DMSO (control) for 2 h and then labeled with 200 μCi of [³⁵S]methionine for 5 min. The synthesis of hsp70, Ydj1p, and Sis1p was measured as for panel A.