Major rearrangement of cellular DNA in the vicinity of integrated polyomavirus DNA

Abstract The Cyp cell line was produced by transforming mouse embryo cells at the restrictive temperature with an early thermosensitive mutant of polyomavirus (Py). Transfer of Cyp cells to the nonrestrictive temperature causes excision to occur at a single chromosomal site carrying viral DNA, and leads to the production of infectious virus. We have attempted to elucidate the recombination event that occurred during the integration of Py DNA in this inducible line. Physical characterization of two recombinant DNAs—one selected from a genomic library of normal mouse DNA and the other constructed from the unoccupied allele of the Cyp integration site—indicates that generation of the Cyp line has involved the joining of not only viral DNA to a cellular α site, but also the cellular α site to a cellular β site. Hence, previously described hybrid excision products from the Cyp line were made of mouse DNA segments representing two distinct cellular sites. The α-β joining may play a role in the expression of integrated Py DNA.