Increased UV resistance in xeroderma pigmentosum group A cells after transformation with a human genomic DNA clone.

Abstract

Xeroderma pigmentosum (XP) is an autosomal recessive disease in which the major clinical manifestation is a 2000-fold enhanced probability of developing sunlightinduced skin tumors, and the molecular basis for the disease is a defective DNA excision repair system. To clone the gene defective in XP complementation group A (XP-A), cDNA clones were isolated by a competition hybridization strategy in which the corresponding mRNAs were more abundant in cells of the obligately heterozygous parents relative to cells of the homozygous proband affected with the disease. In this report, a human genomic DNA clone that contains this cDNA was transformed into two independent homozygous XP-A cell lines, and these transformants displayed partial restoration of resistance to the killing effects of UV irradiation. The abundance of mRNA corresponding to this cDNA appears to correlate well with the observed UV cell survival. The results of unscheduled DNA synthesis after UV exposure indicate that the transformed cells are repair proficient relative to that of the control XP-A cells. However, using this same genomic DNA, transformation of an XP-F cell line did not confer any enhancement of UV survival or promote unscheduled DNA synthesis after UV exposure.

Repair by human cell extracts of single (6-4) and cyclobutane thymine-thymine photoproducts in DNA.

“…One possibility is that the nucleotide excision repair system may recognize or incise each with significantly different efficiencies. Alternatively, there may be two partially redundant repair systems, only one ofwhich efficiently removes photoproducts (14,15). lesions might also be preferentially repaired if they are more accessible in chromatin to the repair complex, a possibility supported by evidence that (6-4) photoproducts (unlike cyclobutane dimers) form with higher yield in linker regions of nucleosomes than in the core (16,17).…”

Repair of Thymine Dimers and (6–4) Photoproducts in Group a Xeroderma Pigmentosum Cell Lines Harboring a Transferred Normal Chromosome 9

“…Lambert and Lambert (1985) also proposed that the defect in XP-A cells could be associated with the abrogation of two independent genes. Recently, Rinaldy et al (1990) isolated a genomic DNA clone which could partially restore UV-resistance when it was introduced into XP-A cells. Comparison of the restriction map of this gene with the pattern of Southern hybridization of the XPAC gene (Rinaldy et al, 1990;Tanaka er al., 1990) suggested that these two genes were not identical.…”

“…Recently, Rinaldy et al (1990) isolated a genomic DNA clone which could partially restore UV-resistance when it was introduced into XP-A cells. Comparison of the restriction map of this gene with the pattern of Southern hybridization of the XPAC gene (Rinaldy et al, 1990;Tanaka er al., 1990) suggested that these two genes were not identical. It is possible that the gene isolated by Rinaldy et al is located on a chromosome other than 9 and defective in our XPZOSSV cells.…”