Removal of uv-induced pyrimidine dimers from the replicated and unreplicated DNA of human fibroblasts Page: 1 of 4
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THE REMOVAL OF UV-INDUCED PYRIMIDN D FRM THE
REPLICATED AND UNREPLICATED DNA OF HUMAN FIBROBLASTSI
Biology Division, Oak Ridge National Laboratory, P.O. Box Y
Oak Ridge, Tennessee 37830
ABSTRACT Excision repair in UV irradiated human fibro-
blasts has been examined in portions of DNA replicating
after irradiation versus those remaining unreplicated. -
Two approaches, one using a UV-endonuclease to estimate u11 1 - a. u D.O. o .
pyrimidine dimers remaining in DNA, the other using . ..
density labeling to measure excision resynthesis, "uw i".rr.,"".Z.
of .iam of ey krorstlim, 9.mwai. po~a o
indicate that the extent of repair is the same for both '
replicated and unreplicated DNA. ."''""""
Studies involving the effects of UV irradiation on DNA
replication in mammalian cells have shown that CHO cells,
which excise only a small percent of the pyrimidine dimers
induced, replicate most of their genome after 5 or 10 J-m2
of UV (1). As the DNA synthesized is larger than interdimer
distance, replication must get past dimers in parental DNA
(2) and, unlike bacteria (3), do so without exchanging many
of the lesions to daughter strands (2).
Various experiments have suggested that DNA replication
in normal human cells reacts similarly (4,2). However,
interpretations of data are difficult for at least three
reasons. First, normal human fibroblasts can excise half of
the dimers induced by 10 J-m-2 UV during twenty four hours
after irradiation (5). Second, after this dose, only half
the amount of DNA is made during this period as compared to
unirradiated cells. Third, DNA replication is affected to
greater extent in UV irradiated excision defective Xeroderma
pigmentosum cells (6). These facts suggest a close correla-
tion between excision and DNA replication. Hence, it was
possible that DNA synthesis seen in UV-irradiated normal
cells only occurred in portions of the genome that had under-
gone excision-repair to remove dimers prior to replication,
or that replicating regions were being preferentially repair-
ed by excision. In order to investigate these possibilities
the repair of both the DNA replicated and that remaining
unreplicated has been monitored at various times following
lResearch sponsored by the Department of Energy under
contract with the Union Carbide Corporation.
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Waters, R. Removal of uv-induced pyrimidine dimers from the replicated and unreplicated DNA of human fibroblasts, article, January 1, 1978; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc1059269/m1/1/: accessed March 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.