Structure of simian virus 40-φX174 recombinant genomes isolated from single cells

Three simian virus (SV40)-φX174 recombinant genomes were isolated from single BSC-1 monkey cells cotransfected with SV40 and φX174 RF1 DNAs. The individual cell progenies were amplified, cloned, and mapped by a combination of restriction endonuclease and heteroduplex analyses. In each case, the 600 to 1,000 base pairs of φX174 DNA (derived from different regions of the φX174 genome) were present as single inserts, located in either the early or late SV40 regions; the deletion of SV40 DNA was greater than the size of the insert; and the remaining portions of the hybrid genome were indistinguishable from wild-type SV40 DNA, as judged by both mapping and biological tests. Hence, apart from the deletion which accommodates the φX174 DNA insert, no other rearrangements of SV40 DNA were detected. The restriction map of a SV40-φX174 recombinant DNA isolate before molecular cloning was indistinguishable from those of two separate cloned derivatives of that isolate, indicating that the species cloned was the major amplifiable recombinant structure generated by a single recombinant-producing cell. The relative simplicity of the SV40-φX174 recombinant DNA examined is consistent with the notion that most recombinant-producing BSC-1 cells support single recombination events generating only one amplifiable recombinant structure.