Expression level of the E1A constructs. SW613-3 cells were transfected with plasmid constructs coding for the indicated wild-type or mutant E1A proteins. Cellular extracts were analyzed by Western blotting with an anti-E1A antibody. (A) N- and C-terminal deletion mutants. The E1A-C29, -C79 and -C109 polypeptides cannot be detected with this antibody. (B) Internal deletion mutants. Note that E1A and some of its mutants are very sensitive to proteolysis (white asterisks) in spite of the presence of protease inhibitors. Similar results were obtained in SW613-B3 cells (not shown).