Xeroderma pigmentosum variants have a slow recovery of DNA synthesis after irradiation with ultraviolet light.
Human cells (normal and xeroderma pigmentosum variant) irradiated with ultraviolet light and pulse-labelled with [3H]thymidine underwent transient decline and recovery of molecular weights of newly synthesized DNA and rates of [3H]thymidine incorporation. The ability to synthesize normal-sized DNA recovered more rapidly in both cell types than thymidine incorporation. During recovery cells steadily increased in their ability to replicate normal-sized DNA on damaged templates. The molecular weight versus time curves fitted exponential functions with similar rate constants in normal and heterozygous xeroderma pigmentosum cells, but with a slower rate in two xeroderma pigmentosum variant cell lines. Caffeine added during the post-irradiation period eliminated the recovery of molecular weights in xeroderma pigmentosum variant but not in normal cells. The recovery of the ability to synthesize normal-sized DNA represents a combination of a number of cellular regulatory processes, some of which are constitutive, and one of which is altered in the xeroderma pigmentosum variant such that recovery becomes slow and caffeine sensitive.
D002110:Caffeine / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis / Q000528:radiation effects*; D004260:DNA Repair / Q000187:drug effects; D004261:DNA Replication / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D008970:Molecular Weight; D014466:Ultraviolet Rays; D014983:Xeroderma Pigmentosum / Q000378:metabolism*
D002110:Caffeine; D004247:DNA