Identification of critical elements within the JC virus DNA replication origin.

The T antigen of JC virus (JCV) does not interact productively with the simian virus 40 (SV40) origin of replication. In contrast, the SV40 T antigen does drive replication from the JCV origin as well as from its own. The basis for this restricted interaction was investigated by analyzing the structure of the JCV replication origin. The replication activities of JCV-SV40 hybrid origin plasmids were tested in cells constitutively producing either the JCV or SV40 T antigen. Results indicated that a region of the JCV origin critical for interaction with the JCV T antigen was positioned to the late side of the central palindrome of the putative core origin. A mutational analysis of this region indicated that the sequence of the A + T-rich tract was primarily responsible for determining the efficiency with which JCV can initiate replication from its origin. The tandemly repeated pentameric sequence AGGGA located proximal to the A + T-rich tract in the JCV enhancer element was found to stimulate JCV, but not SV40, T antigen-mediated replication. The effect on replication of other elements within the JCV enhancer was also dependent on the T antigen employed for initiation. A plasmid containing the replication origin of prototype BK virus was unable to replicate in cells containing JCV T antigen, again indicating the inflexibility of the JCV T antigen in interacting with heterologous origins.