Emp24p, Erv25p, Erp1p, and Erp2p protein levels are interdependent. Total cell extracts from wild-type and p24 mutant cells were separated by SDS-PAGE, and proteins were detected on Western blots using Emp24p, Erv25p, Erp1p, or Erp2p antisera as indicated. A mAb to porin, a mitochondrial membrane protein unrelated to this study, was used as a loading control.