The MLL/MEN chimeric protein binds to p53. (A) Cell extracts derived from COS1 cells transfected with CMVp53, alone or in combination with pME18S-MLL/MEN(FLAG), were immunoprecipitated with anti-FLAG monoclonal antibody (lanes 1 and 2) or with the protein A-Sepharose beads only (lane 3). Western blot was performed using anti-p53 monoclonal antibody (DO-1). Lane 4 contains the total cell lysate (TCL) from COS1 cells transfected with CMVp53 as a control. (B) Cell extracts derived from COS1 cells transfected with CMVp53, alone or in combination with pME18S-MEN(FLAG), were immunoprecipitated with anti-FLAG monoclonal antibody (lanes 1 and 2) or with the protein A-Sepharose beads only (lane 3). Western blot was performed using anti-p53 monoclonal antibody (DO-1). Lane 4 contains the TCL from COS1 cells transfected with CMVp53 as a control. (C) Cell extracts derived from COS1 cells transfected with CMVp53, alone or in combination with pME18S-MEN(HA), were immunoprecipitated with anti-p53 monoclonal antibody (lanes 1 and 2) or with the protein A-Sepharose beads only (lane 3). Western blot was performed using anti-HA polyclonal antibody (HA.11). Cell extracts derived from COS1 cells transfected with pME18S-MEN(HA) were immunoprecipitated with anti-HA polyclonal antibody and subjected to Western blot using anti-HA polyclonal antibody (lane 4) as a control.