Fig. 2. Binding of C-APC fragments to different endogenous N-APC fragments. (A,B) GFP-tagged C-APC or GFP-tagged C1, C2, C3 or C3m fragments were transiently expressed in SW480 (A) or Colo320 (B) cells. Please note that the GFP tag increased the molecular weight of these proteins so that they appear larger than in Fig. 1. Lysates from transfected cells were blotted with a monoclonal anti-GFP antibody (upper panel). The endogenous N-APC was precipitated with a monoclonal anti-N-APC antibody and the bound C-APC fragments were detected using an anti-GFP antibody (middle panel). Cells transfected with GFP alone acted as controls. (C) Purified C3 (C3–His-tag) was immobilised using a polyclonal anti-C-APC antibody. Individual N-APC fragments labelled with ³⁵S-methionine were prepared by in vitro translation and added to the immobilised C3 fragments. Bound N-APC fragments were detected using autoradiography.