Alterations in the structure of new and old forms of simian virus 40 large T antigen (T) defined by age-dependent epitope changes: new T is the same as ATPase-active T.

The reactivity of simian virus 40 large T antigen labeled under pulse-chase conditions towards 22 antibodies was measured. Changes in epitope reactivity occurred in several domains of T as it matured, defining major structural alterations that distinguished mature from new molecules. New T reacted best with the same antibodies that bind and inhibit ATPase-active T. These antibodies thus can distinguish new T as a distinct structural and functional form.