Requirements for Excision and Amplification of Integrated Viral DNA Molecules in Polyoma Virus-Transformed Cells
- 1 August 1982
- journal article
- research article
- Published by American Society for Microbiology in Journal of Virology
- Vol. 43 (2), 617-628
- https://doi.org/10.1128/jvi.43.2.617-628.1982
Abstract
The integration of polyoma virus DNA into the genome of transformed rat cells generally takes place in a tandem head-to-tail arrangement. A functional viral large tumor antigen (T-Ag) renders this structure unstable, as manifested by free DNA production and excision or amplification of the integrated viral DNA. All of these phenomena involve the mobilization of precise genomic units suggesting that they result from intramolecular homologous recombination events occurring in the repeated viral DNA sequences within the integrated structures. Polyoma ts-a-transformed rat cell lines, which produced large T-Ag but contained less than a single copy of integrated viral DNA, were studied. In all of these lines, reversion to a normal phenotype (indicative of excision) was extremely low and independent of the presence of a functional large T-Ag. The revertants were either phenotypic or had undergone variable rearrangements of the integrated sequences that seemed to involve flanking host DNA. In 2 of these cell lines (ts-a 4A and ts-a 3B), no evidence of amplification could be detected even after 2 mo. of propagation under conditions permissive for large T-Ag. An amplification event was detected in a small subpopulation of the ts-a R5-1 line after 2 mo. of growth at 33.degree. C. This involved a DNA fragment of 5.1 kilobases, consisting of the left portion of the viral insertion and .apprx. 2.5 kilobases of adjacent host DNA sequences. None of these lines spontaneously produced free viral DNA, but after fusion with 3T3 mouse fibroblasts, R5-1 and 4A produced a low level of heterogeneous free DNA molecules, which contained both viral and flanking host DNA the ts-a 9 cell line, whose viral insertion consists of a partial tandem of .apprx. 1.2 viral genomes, underwent a high rate of excision or amplification when propagated at temperature permissive for large T-Ag function. Thus, the high rate of excision and amplification of integrated viral genomes observed in polyoma-transformed rat cells requires the presence of regions of homology (i.e., repeats) in the integrated viral sequences. Therefore, these events occur via homologous intramolecular recombination, which is promoted directly or indirectly by the large viral T-Ag.This publication has 33 references indexed in Scilit:
- Recombination between short DNA homologies causes tandem duplicationNature, 1981
- Polyoma large T antigen regulates the integration of viral DNA sequences into the genome of transformed cellsCell, 1981
- The linkage arrangement of four rabbit β-like globin genesCell, 1979
- Untransformed rat cells containing free and integrated dna of a polyoma nontransforming (Hr-t) mutantCell, 1979
- Loss of integrated viral DNA sequences in polyoma-transformed cells is associated with an active viral A functionCell, 1979
- Tumor antigens induced by nontransforming mutants of polyoma virusCell, 1978
- Characterization of t antigens in polyoma-infected and transformed cellsCell, 1978
- Labeling deoxyribonucleic acid to high specific activity in vitro by nick translation with DNA polymerase IJournal of Molecular Biology, 1977
- Detection of specific sequences among DNA fragments separated by gel electrophoresisJournal of Molecular Biology, 1975
- Selective extraction of polyoma DNA from infected mouse cell culturesJournal of Molecular Biology, 1967