FIG. 1.

Immune complexes precipitated by a p300/CBP/p270-reactive antibody. ³⁵S- or ³²P-labeled 293 cell lysates were immunoprecipitated with monoclonal antibody NM1 under nondenaturing conditions (−). To distinguish associated from cross-reactive species, half of the complex was denatured (+) by boiling in SDS and reprecipitated with fresh NM1 in conditions where only proteins directly recognized by the antibodies are recovered. The proteins from each immunoprecipitation were separated by electrophoresis and visualized by autoradiography. The positions of the associated protein species are shown on the right; the positions of p300, CBP, and p270 are shown on the left. The ³⁵S panel is lightly exposed to enhance the resolution of p300, CBP, and p270. Only the bands corresponding to p300, CBP, and p270 are recovered by the antibody after the complex has been denatured.