PPIase activity is required in zpr1 mutant strains. (A) zpr1-1 cpr1Δ (HC12-1A) and zpr1-3 cpr1Δ (HM3) cells, each containing the plasmid pCH1122-CPR1 (CPR1/URA3) and empty vector, pRS415-CPR1, or 2μm vectors containing the indicated PPIase, were plated onto 5-FOA in fivefold serial dilutions. (B) Lysates of wild-type (W1536-5B; WT), cpr1Δ (HC1-2B), and cpr1Δ strains expressing wild-type and mutant hCyPA proteins from the plasmid pRS415 were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotted with anti-hCyPA antibody. Jurkat T-cell lysate was loaded as a control for hCyPA expression. (C) zpr1-1 cpr1Δ (HC12-1A) and zpr1-3 cpr1Δ (HM3) cells, each containing the plasmid pCH1122-CPR1 (CPR1/URA3) and empty vector (pRS415) or pRS415 containing the indicated PPIase, were plated onto 5-FOA in fivefold serial dilutions. Percentages of in vitro PPIase activity relative to that of wild-type hCyPA (35) are indicated. N.A., not applicable.