Western blot using affinity purified anti-SMAD4 to detect over-expressed SMAD4 in transfected COS cells (lane 2). Lane 1 contains lysate from mock transfected COS cells. A doublet band is seen in the SMAD4 transfected lysate with the upper band (arrowhead) representing SMAD4 and the lower band being non-specific staining. The membrane was probed with tprimary antibody at a 1:1,000 dilution.