ATP induces the assembly of polyoma large tumor antigen into hexamers

Using zone velocity sedimentation and nondenaturing polyacrylamide gel electrophoresis, we have determined that purified polyoma large tumor antigen (Py T Ag) consists of discrete forms ranging from more abundant monomers and dimers to several higher but clearly distinguishable oligomeric species. Addition of ATP and MgCl2 to Py T Ag caused a dramatic increase in the appearance of Py T Ag hexamers, a form that, based on its SV40 T Ag counterpart, is likely to play a crucial role in its DNA replication functions. Other nucleotides in addition to ATP, as well as a nonhydrolyzable ATP derivative, were capable of inducing hexamer formation. This approach may further elucidate the role(s) of different forms of Py T Ag in viral regulatory processes.