Defined oligomeric SV40 DNA: A sensitive probe of general recombination in somatic cells

We have constructed well defined oligomeric molecules of simian virus 40 (SV40) DNA as probes for investigating mechanisms by which cultured somatic cells recombine DNA. Restriction enzyme fragments from different temperature-sensitive mutants were joined in a head-to-tail orientation to create partial dimers 1.84 genome lengths in size. These molecules are too large to fit into a viral capsid. Therefore an assay that depends on production of progeny virus after infection with oligomeric DNA is a selective measure of precise conversion of oligomers to monomers. By constructing oligomers from appropriate combinations of temperature-sensitive DNAs, we have been able to study the conversion process in several defined regions of the SV40 genome. Our results indicate that conversion of oligomers to monomers occurs uniformly throughout the genome and is not dependent on normal viral DNA replication. These data indicate that conversion occurs primarily by general, homology-dependent recombination. At least one secondary mechanism that generates a low level of wild-type progeny was also detected. Studies with heteroduplex molecules indicate that repair of mismatched bases may be the secondary mechanism.