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Philos Trans R Soc Lond B Biol Sci. 2018 Jun 5;373(1748). pii: 20170337. doi: 10.1098/rstb.2017.0337.

Excision of the doubly methylated base N4,5-dimethylcytosine from DNA by Escherichia coli Nei and Fpg proteins.

Author information

1
Department of Chemistry, Bioscience and Environmental Technology-Centre for Organelle Research, Faculty of Science and Technology, University of Stavanger, PO Box 8600 Forus, 4021 Stavanger, Norway.
2
Department of Biological DNA Modification, Institute of Biotechnology, Vilnius University, Vilnius 10257, Lithuania.
3
Institute for Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway.
4
Department of Microbiology, Oslo University Hospital, Rikshospitalet, 0372 Oslo, Norway.
5
Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, 0317 Oslo, Norway.
6
Department of Biological DNA Modification, Institute of Biotechnology, Vilnius University, Vilnius 10257, Lithuania saulius.klimasauskas@bti.vu.lt.
7
Department of Chemistry, Bioscience and Environmental Technology-Centre for Organelle Research, Faculty of Science and Technology, University of Stavanger, PO Box 8600 Forus, 4021 Stavanger, Norway svein.bjelland@uis.no.

Abstract

Cytosine (C) in DNA is often modified to 5-methylcytosine (m5C) to execute important cellular functions. Despite the significance of m5C for epigenetic regulation in mammals, damage to m5C has received little attention. For instance, almost no studies exist on erroneous methylation of m5C by alkylating agents to doubly or triply methylated bases. Owing to chemical evidence, and because many prokaryotes express methyltransferases able to convert m5C into N4,5-dimethylcytosine (m N4,5C) in DNA, m N4,5C is probably present in vivo We screened a series of glycosylases from prokaryotic to human and found significant DNA incision activity of the Escherichia coli Nei and Fpg proteins at m N4,5C residues in vitro The activity of Nei was highest opposite cognate guanine followed by adenine, thymine (T) and C. Fpg-complemented Nei by exhibiting the highest activity opposite C followed by lower activity opposite T. To our knowledge, this is the first description of a repair enzyme activity at a further methylated m5C in DNA, as well as the first alkylated base allocated as a Nei or Fpg substrate. Based on our observed high sensitivity to nuclease S1 digestion, we suggest that m N4,5C occurs as a disturbing lesion in DNA and that Nei may serve as a major DNA glycosylase in E. coli to initiate its repair.This article is part of a discussion meeting issue 'Frontiers in epigenetic chemical biology'.

KEYWORDS:

5-methylcytosine methylation damage; DNA base excision repair; N4,5-dimethylcytosine; epigenetics

PMID:
29685966
PMCID:
PMC5915725
[Available on 2019-06-05]
DOI:
10.1098/rstb.2017.0337

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