Jan 1, 1976

DNA single-strand breaks during repair of UV damage in human fibroblasts and abnormalities of repair in xeroderma pigmentosum

Proceedings of the National Academy of Sciences of the United States of America
A J FornaceH E Kann


The method of DNA alkaline elution was applied to a study of the formation and resealing of DNA single-strand breaks after irradiation of human fibroblasts with ultraviolet light (UV). The general features of the results were consistent with current concepts of DNA excision repair, in that breaks appeared rapidly after UV, and resealed slowly in normal fibroblasts, whereas breaks did not appear in those cells of patients with xeroderma pigmentosum (XP) that are known to have defects in DNA repair synthesis. The appearance of breaks required a short post-UV incubation, consistent with the expected action of an endonuclease. Cells of the variant form of XP characterized by normal DNA repair synthesis exhibited normal production of breaks after UV, but were slower than normal cells in resealing these breaks. This difference was enhanced by caffeine. A model is proposed to relate this finding with a previously described defect in post-replication repair in these XP variant cells. DNA crosslinking appears to cause an underestimate in the measurement of DNA breakage after UV.

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Mentioned in this Paper

Base Excision Repair
Xeroderma Pigmentosum
Roentgen Rays
Hydrogen-Ion Concentration
Black Light, Ultraviolet
DNA Repair-Deficiency Disorders
Radiation Genetics
DNA, Single-Stranded
DNA, Double-Stranded

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