Repair-deficient Xeroderma Pigmentosum Cells Research Articles

DNA damage, dna repair and chromosome aberrations of xeroderma pigmentosum cells and controls following exposure to nitrosation products of methylguanidine

Nitrosation of methylguanidine (MG) led to products that caused DNA fragmentation (shift in sedimentation profiles of velocity centrifugation through alkaline sucrose gradients), a DNA repair synthesis (unscheduled uptake of ( 3 H]TdR), chromosome aberrations and a lethal effect of cultured human fibroblasts. The response of repair-deficient xeroderma pigmentosum cells did not differ from that of controls. The nitrosation of MG must be carried out at a pH level below 3, in order to obtain products that react with cellular DNA. The results show that a DNA repair synthesis of human fibroblasts appear to be a sensitive assay for carcinogenic and mutagenic nitrosation products which may be formed within an organism from non-carcinogenic compounds.

Sedimentation of DNA from Human Fibroblasts Irradiated with Ultraviolet Light: Possible Detection of Excision Breaks in Normal and Repair-Deficient Xeroderma Pigmentosum Cells

Usual alkaline sucrose techniques, which produce single-stranded DNA from unirradiated mammalian cells of $2-5\times 10^{8}$ daltons (120-165 S) prove inadequate for resolution of strand breaks transiently present during excision repair of ultraviolet (uv) damage. These breaks seem to be relatively few in number and sedimentation changes are at the limit of resolution. Using a simple modification employing brief lysis in alkali, DNA with sedimentation coefficients up to 350 S have been obtained from human fibroblasts. 350-S DNA from unirradiated fibroblasts consists of complementary strands cosedimenting with choline-labeled material originating in the cytoplasm, in a conformation that allows renaturation to double-stranded DNA on neutralization after gradient fractionation. Large changes in sedimentation coefficient occur immediately after irradiation of normal fibroblasts with doses as low as $5-10 {\rm ergs}/{\rm mm}^{2}$ , but not xeroderma pigmentosum (XP) fi...