Mutants of Drosophila melanogaster which are defective in DNA synthesis have been identified among mutagen-sensitive stocks through analysis of both organ and cell cultures A new procedure employing larval brain ganglia allows poorly fertile or sterile mutants to be analyzed for the first time Parallel studies were performed in both tissues to establish the sensitivity of the new assay relative to that of the proven cell-culture assay Damage was induced in the DNA of cultured cells with UV irradiation and in that of ganglial cells with the carcinogen N-acetoxy-2-acetylaminofluorene Cultures were then pulse-labeled with 3H-thymidine, incubated in the absence of thymidine, and the newly synthesized DNA was analyzed by alkaline sucrose gradient centrifugation The molecular weight of labeled DNA from mutant cells was compared with that from control cells to assess the effect of the mutant on DNA synthesis Among 16 mutant stocks that were scanned in either or both tissues, seven show reductions in DNA synthesis using an undamaged template Mutants at five different genetic loci [mus(2)205, mus(3)304, mus(3)308, mus(3)310 and mus(3)311] possess a reduced capacity to synthesize DNA on a UV-damaged template in primary cell cultures Four of these five defects can also be detected in carcinogen-treated organ cultures Two additional defects in postreplication repair were observed with the brainganglia assay in strains that cannot be assayed in cell culture [mus(1)108, mus(2)206]

Postreplication repair defects in mutants of Drosophila melanogaster.

Postreplication repair has been studied in ultraviolet light (UV)-irradiated fibroblast strains derived from eight apparently normal control donors and seven xeroderma pigmentosum patients. One control donor strain had an intermediate defect in postreplication repair similar to that in excision-deficient xeroderma pigmentosum fibroblasts. However, unlike the xeroderma pigmentosum strains, this control donor strain had normal UV-induced unscheduled DNA synthesis and normal survival after irradiation with UV. This unique fibroblast strain should after irradiation with UV. This unique fibroblast strain should be useful in studies designed to elucidate the possible role of postreplication repair in UV-induced carcinogenesis and mutagenesis.

https://cancerres.aacrjournals.org/content/canres/40/8_Part_1/2736.full.pdf

Human Fibroblast Strain with Normal Survival but Abnormal Postreplication Repair after Ultraviolet Light Irradiation

Postreplication repair is defective in fibroblasts from all the xeroderma pigmentosum (XP) complementation groups with the exception of group E, the defect being most pronounced in the excision-proficient XP variants. It is normal in cells from patients with a variety of other disorders. During postreplication repair pyrimidine dimer sites become associated with daughter strands in both normal and XP cells.

Postreplication Repair in Human Fibroblasts

Cells cultured from most patients suffer- ing from the sunlight-sensitive hereditary disorder xero- derma pigmentosum are defective in the ability to excise ultraviolet light (UV)-induced pyrimidine dimers from their DNA. There is, however, one class of these patients whose cells are completely normal in this excision repair process. We have found that these cells have an abnormal- ity in the manner in which DNA is synthesized after UV- irradiation. The time taken to convert initially low- molecular-weight DNA synthesized in UV-irradiated cells into high-molecular-weight DNA similar in size to that in untreated cells is much greater in these variants than in normal cells. Furthermore, this slow conversion of low to high-molecular-weight newly synthesized DNA is dras- tically inhibited by caffeine, which has no effect in normal cells. Two cell lines from classes of xeroderma pigmento- sunm that are defective in excision-repair show inter- mediate effects, with regard to both the time taken to

C. F. Arlett

Papers

Postreplication Repair in Human Fibroblasts

Xeroderma Pigmentosum Cells with Norm Have a Defect in DNA Synthesis after UV