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Mol. Cell. Biol., Jul 1997, 3779-3785, Vol 17, No. 7
G Henderson and JP Simons
In mammalian cells, the predominant pathway of chromosomal integration of
exogenous DNA is random or illegitimate recombination; integration by
homologous recombination is infrequent. Homologous recombination is
initiated at double-strand DNA breaks which have been acted on by
single-strand exonuclease. To further characterize the relationship between
illegitimate and homologous recombination, we have investigated whether
illegitimate recombination is also preceded by exonuclease digestion.
Heteroduplex DNAs which included strand-specific restriction markers at
each of four positions were generated. These DNAs were introduced into
mouse embryonic stem cells, and stably transformed clones were isolated and
analyzed to determine whether there was any strand bias in the retention of
restriction markers with respect to their positions. Some of the mismatches
appear to have been resolved by mismatch repair. Very significant strand
bias was observed in the retention of restriction markers, and there was
polarity of marker retention between adjacent positions. We conclude that
DNA is frequently subjected to 5'-->3' exonuclease digestion prior to
integration by illegitimate recombination and that the length of DNA
removed by exonuclease digestion can be extensive. We also provide evidence
which suggests that frequent but less extensive 3'-->5' exonuclease
processing also occurs.
Copyright © 1997, American Society for Microbiology
Processing of DNA prior to illegitimate recombination in mouse cells
Department of Anatomy and Developmental Biology, Royal Free Hospital School of Medicine, London, United Kingdom.
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