Misreading of DNA templates containing 8-hydroxydeoxyguanosine at the modified base and at adjacent residues

Our plain-English summary of Misreading of DNA templates containing 8-hydroxydeoxyguanosine at the modified base and at adjacent residues, by Y. Kuchino, F. Mori, H. Kasai, et al (Nature, 1987).

The study

• Authors: Y. Kuchino, F. Mori, H. Kasai, H. Inoue, S. Iwai, K. Miura, E. Ohtsuka, S. Nishimura
• Journal: Nature
• Published: 1987;327(6117):77-9
• Cited by: 702 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

It has been shown previously that deoxyguanosine residues in DNA are hydroxylated at the C-8 position both in vitro and in vivo to produce 8-hydroxydeoxyguanosine (8-OH-dG) by various agents that produce oxygen radicals such as reducing reagents-O2, metal ions-O2, polyphenol-H2O2-Fe3+, asbestos-H2O2 or ionizing radiation. These agents are mostly either mutagenic or carcinogenic; therefore, the formation of 8-OH-dG can also be considered a likely cause of mutation or carcinogenesis by oxygen radicals. It is of interest to know whether the 8-OH-dG residue in DNA is misread during DNA replication. To answer this question, we have examined the effect of the 8-OH-dG residue in DNA on the fidelity of DNA replication using a DNA synthesis system in vitro with Escherichia coli DNA polymerase I (Klenow fragment). The synthetic oligodeoxynucleotides, with or without an 8-OH-dG residue in a specified position, were chemically synthesized and used as templates for DNA synthesis under the conditions of the dideoxy chain termination sequencing method. Surprisingly, in addition to misreading of the 8-OH-dG residue itself, pyrimidines next to the 8-OH-dG residue (G has not yet been tested) were also misread.

In plain English

This was a laboratory experiment on DNA, not a study of people or of asbestos. The authors noted that earlier studies had shown that several agents that produce oxygen radicals, including asbestos combined with hydrogen peroxide, create a damaged DNA unit called 8-hydroxydeoxyguanosine (8-OH-dG). They made short synthetic DNA strands, with or without 8-OH-dG at a set position, and copied them with a bacterial DNA-copying enzyme (E. coli DNA polymerase I, Klenow fragment). When 8-OH-dG sat between T and C (fragment B), it directed insertion of all four DNA bases with almost equal frequency, and the neighbouring C was also misread. An otherwise identical strand with normal G (fragment A) was copied without misreading. When 8-OH-dG sat between A and T (fragment D), it directed only T besides the correct C, while the neighbouring T was misread. The authors concluded that the misreading depends on the surrounding sequence. They also concluded that errors next to the damaged base offer a possible new mechanism of mutation. They stated that whether this happens in living cells was not settled.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: in vitro laboratory experiment (cell-free DNA synthesis using synthetic DNA templates)
• Who was studied: Four chemically synthesized short DNA strands (fragments A, B, C and D), two containing 8-OH-dG (B and D) and two control strands with normal G (A and C), copied by E. coli DNA polymerase I (Klenow fragment); work done at the National Cancer Center Research Institute, Tokyo, and Hokkaido University, Sapporo, Japan; published 1987
• Exposure: A single 8-OH-dG residue placed at a specified position in the DNA template. Asbestos was not tested; asbestos with hydrogen peroxide was mentioned only as one of several agents that earlier studies showed produce 8-OH-dG.
• Main results:
  • In fragment B (8-OH-dG between T and C), the 8-OH-dG directed insertion of A, T, C or G with almost equal frequency
  • In fragment B, the C next to the 8-OH-dG (on its 3' side) also directed insertion of all four bases; the T on the 5' side directed insertion of C and T to a small extent in addition to correct A
  • The control fragment A, with normal G in place of 8-OH-dG, was copied without any misreading under the same conditions
  • In fragment D (8-OH-dG between A and T), the 8-OH-dG directed insertion of only T besides the correct C; the T on its 3' side directed insertion of all four bases, while the A on its 5' side was read correctly
  • In a test without dideoxynucleoside triphosphates (fragments A and B), the authors reported that misreading around 8-OH-dG and its neighbouring bases was still evident, although 'not so clear'
• The authors' conclusion: The authors concluded that the extent of misreading depends on the DNA sequence surrounding 8-OH-dG, and that the loss of copying accuracy at positions next to the damaged base provides a possible new molecular mechanism of mutation
• Limitations the authors state:
  • The experiments only represent effects in a test-tube system; whether the misreading occurs in living cells was not determined
  • The effect of a G next to 8-OH-dG had not been tested
  • The molecular mechanism by which 8-OH-dG affects copying accuracy was unknown

Topics

Medical terms in this study, explained in our Lexicon: Carcinogenic, Carcinogenesis.

Related studies

• Iron-dependent formation of 8-hydroxydeoxyguanosine in isolated DNA and mutagenicity in Salmonella typhimurium TA102 induced by crocidolite — S.P. Faux, P.J. Howden, et al. (1994)
• Patterns of 8-hydroxydeoxyguanosine formation in DNA and indications of oxidative stress in rat and human pleural mesothelial cells after exposure to crocidolite asbestos — H. Fung, Y.W. Kow, et al. (1997)
• Determination of carcinogenic potential of mineral fibers by 8-hydroxydeoxyguanosine as a marker of oxidative DNA damage in mammalian cells — N. Murata-Kamiya, T. Tsutsui, et al. (1997)
• Formation of 8-hydroxydeoxyguanosine by asbestos and man made mineral fibres — P. Leanderson, P. Söderkvist, et al. (1988)
• Glutathione modulates the formation of 8-hydroxydeoxyguanosine in isolated DNA and mutagenicity in Salmonella typhimurium TA100 induced by mineral fibres — P.J. Howden, S.P. Faux (1996)
• Induction of 8-hydroxydeoxyguanosine by man made vitreous fibres and crocidolite asbestos administered intraperitoneally in rats — C. Schürkes, W. Brock, et al. (2004)

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