title: Size and frequency of gaps in newly synthesized DNA of xeroderma pigmentosum human cells irradiated with ultraviolet light.
abstract: Native newly synthesized DNA from human cells (xeroderma pigmentosum type) irradiated with ultraviolet light releases short pieces of DNA (L-DNA) when incubated with the single-strand specific S1 nuclease. This is not observed in the case of unirradiated cells. Previous experiments had shown that the L-DNA resulted from the action of S1 nuclease upon gaps, i.e., single-stranded DNA discontinuities in larger pieces of double-stranded DNA. We verified that the duplex L-DNA, that arises from the inter-gap regions upon S1 nuclease treatment, has a size which approximates the distance between two pyrimidine dimers on the same strand; this has been observed at different fluences of ultraviolet-light and indicates that the gap is related to or opposite the dimer. A method was devised to measure the size of the gaps. A Poisson distribution analysis of the percentage of the L-DNA produced as a function of S1 nuclease concentration made this possible. 65% of the gaps corresponded to stretches of 1,250 nucleotides and 35% to stretches of 150 nucleotides. These parameters have been considered in the proposition of a model for DNA synthesis on a template containing pyrimidine dimers.
mesh_terms: D002472:Cell Transformation, Viral; D004247:DNA / Q000378:metabolism / Q000528:radiation effects*; D004277:DNA, Single-Stranded / Q000378:metabolism / Q000528:radiation effects; D003851:Deoxyribonucleases / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D011336:Probability; D013539:Simian virus 40; D014466:Ultraviolet Rays; D014983:Xeroderma Pigmentosum / Q000648:ultrastructure*
chemical_list: D004277:DNA, Single-Stranded; D004247:DNA; D003851:Deoxyribonucleases