Coactivation of ERα/Sp1 by DRIP150 mutants and interactions of pET28b(+)-131 aa with ERα and Sp1. Coactivation of ERα/Sp1 by DRIP150 deletion mutants (A - C). ZR-75 cells were transfected with pSp13, ERα, wild-type and variant DRIP150 expression plasmids, treated with DMSO or 10 nM E2, and luciferase activity was determined as described in the Materials and Methods. Significant (p < 0.05) coactivation by wild-type or variant DRIP150 constructs are indicated (**). Coimmunoprecipitation of 35S-pET28b(+)-131aa with ERα and Sp1 (D, E). 35SLabled proteins were in vitro expressed, coincubated, immunoprecipitated with Sp1 or ERα antibodies, and immunoprecipitates were analyzed by SDS-PAGE as described in the Materials and Methods.