FIG. 3.

B-ZIP mutations alter the ability of Meq to form homo- and heterodimers. Analysis was performed after the transfection of DF-1 cells with the expression vectors indicated. (A) Meq proteins containing the putative dimerization mutations N-terminally tagged with either HA or Myc epitopes were subjected to immunoprecipitation with a rabbit anti-HA or a control antibody. After SDS-PAGE and Western blotting (WB), they were probed with an anti-Myc antibody. (B) Untagged Meq mutants were immunoprecipitated with rabbit anti-Meq or a control antibody and detected, after Western blotting, with anti-c-Jun antibody. UT indicates untransfected cells expressing no Meq. Only Meq^BZIP failed to bind c-Jun. Because a large excess of control rabbit anti-mouse antibody was used, it is seen as a cross-reactive band in the five central lanes. (C) Similar analysis showed that B-ZIP dimerization mutations have no effect on the interaction between chicken CtBP (chCtBP1) and Meq. After transfection of Meq^WT, Meq^Hom, or Meq^BZIP, all proteins coimmunoprecipitated equally efficiently with endogenous CtBP.