A Cis-acting Sequence Promotes Removal of Simian Virus 40 DNA from the Replication Pool

Pulse-labeled simian virus 40 (SV40) DNA is removed from the pool of molecules available for replication (i.e., it ceases to reenter replication) a few hours after synthesis. We studied this cessation of reentry with mutants containing different deletions in the structural genes of SV40. The DNAs of two independent deletion mutants, dl-1007 (24% deletion) and dl-1003 (8% deletion), were used as templates for further DNA synthesis (i.e., they reentered replication) to a greater extent than was wild-type DNA. The alteration in reentry kinetics was not because the DNAs were smaller; other deletion mutations that were from 76 to 85% of the length of wild-type DNA (dl-BE and dl-1133 with a deletion in the late region and F8dl with a deletion in the early region) did not reenter replication to a greater extent than the wild type did. Cotransfection experiments showed that the mutant phenotypes of dl-1007 and dl-1003 were poorly complemented, if at all, by the wild type. Thus, we propose that there is a cis-acting sequence located in the HindIII E fragment of SV40, not present in either of these mutants, that promotes the efficient removal of DNA from the replication pathway.