cis-acting sequences that control the level of viral DNA synthesis in the polyomavirus late region.

A deletion in the polyomavirus late region results in a drastic reduction of viral replication, as shown after transfection of viral DNA into 3T6 cells. This mutation is cis acting, since cotransfection with wild-type DNA did not restore the normal phenotype. Viral DNA synthesis returned to normal levels only after reintroduction of the authentic sequences in either orientation. The data presented here suggest that these sequences are involved in the binding of a factor(s) that controls the level of viral replication.