Figure 2.

Specificity of the coimmunoprecipitation assay. 293 cells were transfected with plasmids encoding PS1 plus (A) SC35 bearing a myc epitope tag, (B) IκBα, or (C) APP. Cells were lysed in SDS buffer and analyzed directly (crude lysate), or in coimmunoprecipitation lysis buffer and immunoprecipitated with the indicated antibody. Precipitating proteins were immunoblotted with α-myc (A and D), α-IκBα (B), or α-APP (C). (D) A brief exposure of Notch1 coimmunoprecipitated with endogenous PS1 is given for comparison. In all samples, crude lysate equals 20% of the total protein assayed by immunoprecipitation.