title: Mycobacterium smegmatis RqlH defines a novel clade of bacterial RecQ-like DNA helicases with ATP-dependent 3'-5' translocase and duplex unwinding activities.
abstract: The Escherichia coli RecQ DNA helicase participates in a pathway of DNA repair that operates in parallel to the recombination pathway driven by the multisubunit helicase-nuclease machine RecBCD. The model mycobacterium Mycobacterium smegmatis executes homologous recombination in the absence of its helicase-nuclease machine AdnAB, though it lacks a homolog of E. coli RecQ. Here, we identify and characterize M. smegmatis RqlH, a RecQ-like helicase with a distinctive domain structure. The 691-amino acid RqlH polypeptide consists of a RecQ-like ATPase domain (amino acids 1-346) and tetracysteine zinc-binding domain (amino acids 435-499), separated by an RqlH-specific linker. RqlH lacks the C-terminal HRDC domain found in E. coli RecQ. Rather, the RqlH C-domain resembles bacterial ComF proteins and includes a phosphoribosyltransferase-like module. We show that RqlH is a DNA-dependent ATPase/dATPase that translocates 3'-5' on single-stranded DNA and has 3'-5' helicase activity. These functions inhere to RqlH-(1-505), a monomeric motor unit comprising the ATPase, linker and zinc-binding domains. RqlH homologs are distributed widely among bacterial taxa. The mycobacteria that encode RqlH lack a classical RecQ, though many other Actinobacteria have both RqlH and RecQ. Whereas E. coli K12 encodes RecQ but lacks a homolog of RqlH, other strains of E. coli have both RqlH and RecQ.
authors.affiliation: Molecular Biology Program, Sloan-Kettering Institute, NY 10065, USA.
authors.forename: Heather
authors.initials: H
authors.lastname: Ordonez
authors.forename: Mihaela
authors.initials: M
authors.lastname: Unciuleac
authors.forename: Stewart
authors.initials: S
authors.lastname: Shuman
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000145:classification / Q000378:metabolism*; D004247:DNA / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000378:metabolism; D007700:Kinetics; D008670:Metals / Q000378:metabolism; D008969:Molecular Sequence Data; D020102:Mycobacterium smegmatis / Q000201:enzymology*; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D053484:RecQ Helicases / Q000737:chemistry / Q000145:classification* / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D004277:DNA, Single-Stranded; D008670:Metals; D000255:Adenosine Triphosphate; D004247:DNA; D053484:RecQ Helicases