Figure 3.

p23 homologs interact with IRs and affect their activities. (A) Effects of p23, tsp23, or Sba1p on the transcriptional activities of IRs in S. cerevisiae strain (YNK233; Δp23) bearing a disrupted SBA1 gene. The Δp23 strain carried expression plasmids for GR, PR, MR, ER, or TR and were cotransformed with a LEU2 marker plasmid (open bar) or an expression vector for Sba1p (solid bar), p23 (stippled bar), or tsp23 (hatched bar). All transformants carried a reporter plasmid with the appropriate response elements driving a CYC1–lacz fusion. Data were normalized to the activity of the Δp23 strain carrying the LEU2 marker plasmid and represent the average values from three independent assays; error bars, s.e.m.. (B) Association of Sba1p (s), p23 (p), tsp23 (ts), and Hsp82 with IRs. Following growth in the appropriate selective medium and exposure to 10 μm corticosterone where indicated, cell extracts were prepared by glass-bead homogenization and clarification by centrifugation. The GR, MR, or control protein c-Jun was precipitated from 250 μg of protein extract using antibodies specific for each factor. The reactions were subjected to 12% SDS-PAGE, electroblotted to Immobilon-P, and the indicated proteins detected by immunoblotting.