Asp-286----Asn-286 in polyomavirus large T antigen relaxes the specificity of binding to the polyomavirus origin.

We isolated revertants of a polyomavirus whose origin of DNA replication contains a point mutation in the palindrome to which large T antigen binds. Four independent second-site revertants contain an Asp-286----Asn-286 substitution in large T antigen. This mutant large T antigen activates replication of DNAs containing the mutant polyomavirus origin as well as replication of DNAs containing the wild-type origin; however, replication of DNAs with enhancer mutations is not activated by this large T antigen. The Asn-286 mutation occurs in a positively charge region of large T antigen near the location of several mutations which inactivate DNA replication. We suggest that this region of large T antigen is responsible for recognition of specific DNA sequences at the origin and that ionic forces are important for this interaction.