A mechanism for deletion formation in DNA by human cell extracts: the involvement of short sequence repeats.
DNA molecules carrying a site-specific double-strand break were exposed to nuclear extracts from human cell lines. It was shown previously that breaks could be rejoined correctly by human extracts, but that a proportion of the rejoined molecules had suffered deletions and insertions. The 'mis-rejoined' proportion was higher with cell extracts from an individual with the disorder ataxia-telangiectasia than with normal cell extracts. We now show by sequence analysis that deletions in extract-treated molecules occur exclusively between short direct repeats (2-6 base pairs). A mis-rejoined molecule containing an insertion of 300 bp also had a repeat-based deletion at the same site. A number of different direct repeats are involved; however, some clustering of these occurs especially on the upstream side of the initial breakpoint. These data are most simply interpreted in terms of a model of deletion formation involving single-strand exposure and repair, perhaps with the action of other DNA-metabolising enzymes influencing the frequency with which some repeats are involved.
Thacker
J
J
MRC Radiobiology Unit, Didcot, Oxon, UK.
Chalk
J
J
Ganesh
A
A
North
P
P
D001260:Ataxia Telangiectasia / Q000235:genetics; D001483:Base Sequence; D002457:Cell Extracts; D002460:Cell Line; D004247:DNA / Q000378:metabolism*; D004260:DNA Repair; D006801:Humans; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D016133:Polymerase Chain Reaction; D012091:Repetitive Sequences, Nucleic Acid; D017422:Sequence Analysis, DNA; D017384:Sequence Deletion
D002457:Cell Extracts; D004247:DNA