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High-frequency recombination mediated by polyomavirus large T antigen defective in replication
L St-Onge1, L Bouchard, M Bastin
1Department of Biochemistry, University of Sherbrooke, Quebec, Canada.
Journal of Virology
|April 1, 1993
Summary
Polyomavirus and simian virus 40 large T antigens (T-Ag) significantly enhance homologous recombination in mammalian cells. This T-Ag recombination activity is distinct from its viral DNA replication function.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- The large T antigen (T-Ag) of polyomavirus and simian virus 40 (SV40) is known to play roles in viral replication and cellular transformation.
- The precise mechanisms by which T-Ag influences host cell genetic processes, particularly homologous recombination, remain incompletely understood.
Purpose of the Study:
- To investigate the role of polyomavirus and SV40 large T antigens (T-Ag) in promoting homologous recombination in mammalian cells.
- To determine if T-Ag's recombination-promoting activity is linked to its viral DNA replication function.
Main Methods:
- Construction of a rat cell line (Hy5) containing direct repeats of a mutated polyomavirus middle-T-Ag (pmt) oncogene.
- Selection for transformed cell populations resulting from intrachromosomal recombination events.
- Analysis of recombination events including gene conversion, chromosomal inversion, and unequal sister chromatid exchange.
- Assessment of T-Ag's effect on recombination rates and comparison with replication-defective mutants.
Main Results:
- Spontaneous intrachromosomal recombination (gene conversion) of pmt occurred at a low rate (1.7 x 10^-7 per cell generation).
- Polyomavirus large T-Ag significantly increased recombination rates, including chromosomal inversion mediated by pBR322 sequences, by several orders of magnitude.
- T-Ag also promoted unequal sister chromatid exchange, generating chromosomal aberrations relevant to cell transformation.
- Recombination promotion was observed even with T-Ag mutants defective in viral DNA synthesis initiation.
Conclusions:
- Polyomavirus and SV40 large T-Ag possess a potent recombination-promoting activity in mammalian cells.
- This recombination-promoting function of T-Ag is separable from its viral DNA replication capabilities.
- T-Ag-induced recombination can lead to genetic alterations associated with cellular transformation.