Recombination in adenovirus. I. Analysis of recombinant viruses under non-selective conditions

A method is described, based on an approach previously employed for the mapping of adenovirus ts mutants (Grodzicker et al. 1975), for the identification of recombinant viruses in the progeny of mixed infections of human HeLa cells with wild-type adenovirus types 2 and 5 under non-selective conditions. Differences in restriction enzyme sites for the endonuclease HpaI could be used to detect new recombinant DNA fragments in a yield of 3 to 6% after single mixed infections and yields up to 25% following three successive mixed infections. The recombinant nature of the new fragments was proved by the clonal isolation of recombinant viruses in similar yields. Analysis of one cloned recombinant pointed to the occurrence of multiple crossover events at different sites along the virus chromosome. The results are discussed in terms of a biochemical approach towards the study of the mechanism of general genetic recombination in human cells as well as with respect to the evolution of adenoviruses.