CIRCULAR AND LINEAR SIMIAN VIRUS-40 DNAS DIFFER IN RECOMBINATION

Linear forms of SV40 DNA, when added to transfection mixtures containing circular SV40 and .vphi.X174 RFI DNA, enhanced the frequency of SV40/.vphi.X174 recombination, as measured by infectious center in situ plaque hybridization in monkey BSC-1 cells. The sequences required for the enhancement of recombination by linear DNA reside within the SV40 replication origin/regulatory region (nucleotides 5171-5243/0-128). Linearization of .vphi.X174 RFI DNA did not increase the recombination frequency. The SV40/.vphi.X174 recombinant structures arising from transfections supplemented with linear forms of origin-containing SV40 DNA contained .vphi.X174 DNA sequences interspersed within tandem head-to-tail repeats derived from the recombination-enhancing linear DNA. Evidence is presented that the tandem repeats are not formed by homologous recombination and that linear forms of SV40 DNA must compete with circular SV40 DNA for the available T antigen to enhance recombination. Evidently, the enhancement of recombination by linear SV40 DNA results from the entry of that DNA into a rolling circle type of replication pathway which generates highly recombinogenic intermediates.