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An excision event that may depend on patchy homology for site specificity
Abstract:
In mouse cells transformed by a mutant polyomavirus genome, recombination between integrated viral DNA and flanking cellular DNA resulted in the excision of two readily amplifiable chimeras, designated RmI and RmII. The crossing-over that generated RmII was unique in that it involved a simple cellular sequence in which the triplet 5'-CTG-3' was repeated many times. We show that the sequence across the junction resulting from excision was identical in several molecules of RmII, as if the cross-over generating this junction always involved exactly the same two sites on the viral and cellular DNA. We also show that the cellular site mapped where the replacement of a G by an A in one of many successive 5'-CTG-3' triplets generated a homology of five nucleotides (5'-CTACT-3') with the viral site. Oligonucleotides on both sides of these sites are probably involved in matching the two DNAs prior to recombination.
Insights
Recombination in mouse cells excised viral DNA chimeras. A specific DNA sequence with repeated triplets (5'-CTG-3') was key to generating one chimera (RmII), suggesting precise recombination sites.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- Polyomavirus DNA integration into host cells can lead to complex genomic rearrangements.
- Understanding viral-cellular DNA recombination is crucial for deciphering genome stability and viral oncogenesis.
Purpose of the Study:
- To investigate the mechanisms of DNA recombination between integrated polyomavirus and host mouse cell DNA.
- To characterize the structure and formation of amplified chimeric DNA molecules resulting from this recombination.
Main Methods:
- Analysis of DNA sequences from transformed mouse cells.
- Identification and characterization of excision products (chimeras RmI and RmII).
- Sequence comparison across multiple RmII molecules to identify conserved junctional sites.
Main Results:
- Recombination resulted in the excision of two amplifiable chimeric DNA molecules, RmI and RmII.
- The formation of RmII involved a unique cellular sequence characterized by multiple repeats of the 5 '-CTG-3 ' triplet.
- The recombination junction in RmII was highly conserved, indicating precise crossover events.
- The specific cellular recombination site was identified as a sequence with homology (5 '-CTACT-3 ') to the viral site, arising from a single nucleotide substitution within the CTG repeats.
Conclusions:
- Specific repetitive DNA sequences in the host genome can facilitate precise viral-cellular DNA recombination.
- The findings suggest that short oligonucleotide sequences flanking the recombination sites play a role in DNA matching and homologous recombination.
- This study provides insights into the molecular mechanisms underlying viral DNA integration and excision events.