Introduction
Lhr (L arge h elicase-r elated) proteins are
ATP-dependent 3’ to 5’ DNA translocases within the Superfamily 2
helicases [1]. The founder member of Lhr proteins was identified in
bacteria [2], and subsequently Lhr was found to be widely
distributed across all clades of archaea [3]. High amino acid
sequence identity (typically about 30%) between archaeal and bacterial
Lhr proteins is limited to 800-900 amino acids that form helicase
domains from the Lhr N-terminus called the ‘Lhr-Core’ [4].
Biochemical analyses of the Lhr-Core from the bacteriaMycobacterium smegmatis and Pseudomonas putida and from
the archaeon Methanothermobacter thermautotrophicus have
characterized Lhr translocation and helicase mechanism [5-7], and
crystal structures of Lhr-Cores highlight similarities with
translocation by the archaeal DNA repair helicase Hel308 [6, 8],
especially in interactions between their winged helix and RecA-like
domains [9, 10].
In addition to the Lhr-Core, bacterial Lhr proteins extend to 1400-1600
amino acids, in a C-terminal protein region of unknown function, called
Lhr-CTD (Lhr-C-terminal domains). Structural modelling of the bacterial
Lhr-CTD [11] and a subsequent cryo-EM structure [12], provided
intriguing clues to Lhr-CTD function, including the presence of an array
of tandem winged helix domains characteristic of the HTH_42 superfamily
of proteins that have structural homology to the DNA glycosylase AlkZ
[11]. Genetic analyses of the effects on bacterial and archaeal
cells of deleting the lhr gene revealed mild sensitivities to
agents that cause replication stressUV irradiation [13] and
azidothymidine (AZT) [14] and transcriptional up-regulation oflhr in response to mitomycin C [15]. In this work we report
new insights about how Lhr contributes to DNA repair in bacteria. We
demonstrate that the E. coli Lhr protein has uracil-DNA
glycosylase activity, in addition to its well-characterized
ATP-dependent DNA translocase functions, and that cells lacking Lhr are
sensitive to oxidative stress.