AUTHOR=Grøsvik Kristin , Tesfahun Almaz Nigatu , Muruzábal-Lecumberri Izaskun , Haugland Gyri Teien , Leiros Ingar , Ruoff Peter , Kvaløy Jan Terje , Knævelsrud Ingeborg , Ånensen Hilde , Alexeeva Marina , Sato Kousuke , Matsuda Akira , Alseth Ingrun , Klungland Arne , Bjelland Svein 

TITLE=The Escherichia coli alkA Gene Is Activated to Alleviate Mutagenesis by an Oxidized Deoxynucleoside

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.00263

DOI=10.3389/fmicb.2020.00263

ISSN=1664-302X

ABSTRACT=<p>The cellular methyl donor <italic>S</italic>-adenosylmethionine (SAM) and other endo/exogenous agents methylate DNA bases non-enzymatically into products interfering with replication and transcription. An important product is 3-methyladenine (m<sup>3</sup>A), which in <italic>Escherichia coli</italic> is removed by m<sup>3</sup>A-DNA glycosylase I (Tag) and II (AlkA). The <italic>tag</italic> gene is constitutively expressed, while <italic>alkA</italic> is induced by sub-lethal concentrations of methylating agents. We previously found that AlkA exhibits activity for the reactive oxygen-induced thymine (T) lesion 5-formyluracil (fU) <italic>in vitro</italic>. Here, we provide evidence for AlkA involvement in the repair of oxidized bases by showing that the adenine (A) ⋅ T → guanine (G) ⋅ cytosine (C) mutation rate increased 10-fold in <italic>E. coli</italic> wild-type and <italic>alkA</italic><sup>–</sup> cells exposed to 0.1 mM 5-formyl-2′-deoxyuridine (fdU) compared to a wild-type specific reduction of the mutation rate at 0.2 mM fdU, which correlated with <italic>alkA</italic> gene induction. G⋅C → A⋅T alleviation occurred without <italic>alkA</italic> induction (at 0.1 mM fdU), correlating with a much higher AlkA efficiency for fU opposite to G than for that to A. The common keto form of fU is the AlkA substrate. Mispairing with G by ionized fU is favored by its exclusion from the AlkA active site.</p>