期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1978
卷号：75
期号：7
页码：3037-3041
DOI：10.1073/pnas.75.7.3037
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The effect of UV irradiation on the extent and fidelity of DNA synthesis in vitro was studied by using homopolymers and primed single-stranded {phi}X174 phage DNA as substrates. Unfractionated and fractionated cell-free extracts from Escherichia coli pol+ and polA1 mutants as well as purified DNA polymerase I were used as sources of enzymatic activity. (DNA polymerases, as used here, refer to deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7 .) The extent of inhibition of DNA synthesis on UV-irradiated {phi}X174 DNA suggested that pyrimidine dimers act as an absolute block for chain elongation by DNA polymerases I and III. Experiments with an irradiated poly(dC) template failed to detect incorporation of noncomplementary bases due to pyrimidine dimers. A large increase in the turnover of nucleoside triphosphates to free monophosphates during synthesis by DNA polymerase I on irradiated {phi}X174 DNA has been observed. We propose that this nucleotide turnover is due to idling by DNA polymerase (i.e., incorporation and subsequent excision of nucleotides opposite UV photolesions, by the 3'[->]5' "proofreading" exonuclease) thus preventing replication past pyrimidine dimers and the potentially mutagenic event that should result. In support of this hypothesis, DNA synthesis by DNA polymerase from avian myeloblastosis virus and by mammalian DNA polymerase , both of which are devoid of any exonuclease activity, was found to be only partially inhibited, but not blocked, by UV irradiation of the template and accompanied by an increased incorporation of noncomplementary nucleotides. It is suggested that UV mutagenesis in bacteria requires an induced modification of the cellular DNA replication machinery, possibly an inhibition of the 3'[->]5' exonuclease activity associated with DNA polymerases.
关键词：pyrimidine dimers ; DNA polymerases ; proofreading exonuclease ; misincorporation
