Expression of Rap1GAP2 protein. COS-1 cells transiently transfected without or with epitope-tagged Rap1GAP2 or Rap1GAP1, isolated peripheral blood lymphocytes, and isolated washed human platelets were lysed in SDS-containing stop solution. Total protein was separated by SDS-PAGE and immunoblotted with rabbit antiserum against an N-terminal peptide derived from Rap1GAP2 (left) or with an antibody specific for Rap1GAP1 (right). Arrows indicate tagged overexpressed (95 kDa) and endogenous Rap1GAP2 (90 kDa). The antiserum cross-reacts with an unknown protein of 110 kDa. Platelets, and to a lesser extent lymphocytes, contain endogenous Rap1GAP2 but not Rap1GAP1 protein. Shown are examples of experiments performed at least 4 times.