HEK 293 cells were transfected with the C1a-FLAG cDNA alone or in combination with GFP-tagged C1a, Δe13, C1aΔ397, or C1aΔ374, as indicated. Thirty-six to 48 h after transfection, the cells were lysed and the CTR-GFP construct was immunoprecipitated (IP) using the monoclonal anti-GFP antibody. The immune complexes were immunoblotted (IB) with the anti-FLAG antibody (upper panel). The membrane was stripped and reblotted with the anti-GFP antibody (middle panel). To show equal amounts of the FLAG-tagged CTR construct in the different lysates, total cell lysates (TCL) were immunoblotted with the anti-FLAG antibody (lower panel). Identical results were obtained in three independent experiments.