The YsaC secretin coimmunoprecipitates with Psp effector proteins. (A) Φ(pspA-lacZ) operon fusion expression. All strains had the chromosomal pspA operon controlled by the tac promoter and either pspB, pspC, or neither (untagged) modified to encode a C-terminal 3×FLAG epitope tag, as indicated. Strains also contained empty araBp expression plasmid pBAD33 (−YsaC) or a derivative encoding YsaC-His6 (+YsaC). Error bars indicate the positive standard deviations from the means. (B) Immunoblot analysis of input lysates and coimmunoprecipitates (anti-flag IP) derived from the +YsaC strains used in the experiment summarized in panel A. PspA, PspB, PspC, and FtsH were detected with polyclonal antisera, and YsaC-His6 was detected with anti-His6 monoclonal antibody. Approximate positions of molecular mass marker proteins (in kilodaltons) are indicated on the left.