Abnormal Kinetics of DMA Synthesis in Ultraviolet Light-irradiated Cells from Patients with Cockayne's Syndrome1

Cells from patients with the hereditary disorder Cockayne's syndrome and from the sun-sensitive individual, 11961, are sensitive to the lethal effects of ultraviolet light (UV) but have no detectable defect in either excisionor postreplication repair after UV irradiation. In normal cells and in Cockayne hétéro zygotes, UV causes a depression in the rate of DNA-replicative synthesis followed by a recovery of normal rates 5 to 8 hr after irradiation. In Cockayne and 11961 cells, the initial depression in DMA synthesis is the same as that in normal cells, but no subsequent recovery is observed. The recovery of DNA synthesis in normal cells appears to be unaffected by fluorodeoxyuridine but inhibited by cycloheximide. This suggests a possible requirement for de novo protein synthesis, but there are a number of alternative interpretations of these data.