Homologous recombination of polyoma virus DNA in mouse cells

We have produced nonviable deletion mutants of polyoma virus in order to study homologous recombination after DNA transfection into mouse cells. The frequency of recombination was determined by the formation of infectious virus. It was dependent on the amount of DNA transfected and the size of the region of homology between the mutations. Recombination frequencies were highest when both mutated genomes were transfected in closed circular form rather than after linearization of one or both of the recombination partners. The system described may be useful for a more detailed analysis of physiological and genetic conditions influencing the frequency of homologous recombination in mouse cells as well as to study enzymes involved and intermediates produced in this process.