DNA replication origin of polyoma virus: early proximal boundary

We constructed a series of deleted polyoma genomes by Bal 31 nuclease digestion from the unique Bg/I site at nucleotide 86 on the "early" side of the origin of DNA replication. The ability of the cloned deleted genomes to replicate was tested after transfection into mouse 3T6 fibroblasts or into the polyomatransformed C127 (COP5) mouse cell line (Tyndall et al., Nucleic Acids Res. 9:6231-6251, 1981). Deletions up to nucleotide 64-had no effect on the amount of replicated DNA accumulated, but larger deletions, extending up to nucleotide 42, decreased this amount 7- to 10-fold. By nucleotide 38, the quantity of detected DNA was down 100-fold, and by nucleotide 20, no replication could be detected. The minimum origin segment does not contain any known high-affinity, large tumor antigen binding site.