THE DNA-BINDING DOMAIN OF SIMIAN VIRUS-40 TUMOR-ANTIGEN HAS MULTIPLE FUNCTIONS

The DNA-binding domain of simian virus 40 tumor antigen has been previ ously shown to participate in a number of different activities. Beside s being involved in binding to sequences at the viral replication orig in, this domain appears to be required for nonspecific DNA binding, fo r structurally distorting origin DNA (melting and untwisting), and pos sibly for oligomerization of the protein into hexamers and double hexa mers. We now provide evidence that it also takes part in unwinding ori gin DNA sequences, contributes a function specifically related to in v ivo DNA replication, and perhaps supports the assembly of the virus or release of the virus from the cell. This 100-amino-acid domain appear s to be an excellent model system for studying how a small region of a protein could have a number of distinct activities.