Figure 1.

(A) RB can bind E2F1 and hbrm simultaneously. U2OS cells were transfected with 6 μg of the indicated expression vectors and 6 μg of DP1 expression vector. Whole-cell extracts were then immunoprecipitated using either a HA or a E1A antibody as indicated. Immunoprecipitates were assayed by Western blot analysis for the presence of hbrm (Top), RB (Middle), and E2F1 (Bottom) proteins. (B) hbrm/BRG-1 are associated with E2F1 in vivo. WI-38 cells were lysed in IP0.1 buffer and immunoprecipitated either in the absence (lane 3) or in the presence (lane 4) of anti-hbrm/BRG-1 antibodies from rabbit. Control immunoprecipitations were also performed in the presence of WI-38 extract and pre-immune serum (lane 5) and in the presence of anti-hbrm/BRG-1 antibodies, in the absence of WI-38 extract (lane 2). After analysis by 6% PAGE, proteins were transferred to nitrocellulose membrane and analyzed by Western blot with either anti-hbrm/BRG-1 antibodies from chicken (Upper) or an anti-E2F1 monoclonal antibody (Lower).