Escherichia coli RecQ protein is a DNA helicase.

Abstract

The Escherichia coli recQ gene, a member of the RecF recombination gene family, was set in an overexpression plasmid, and its product was purified to near-homogeneity.The purified RecQ protein exhibited a DNA-dependent ATPase and a helicase activity. Without DNA, no ATPase activity was detected. The capacity as ATPase cofactor varied with the type of DNA in the following order: circular single strand > linear single strand >» circular or linear duplex. As a helicase, RecQ protein displaced an annealed 71-base or 143-base singlestranded fragment from circular or linear phage M13 DNA, and the direction of unwinding seemed to be 3' --5' with respect to the DNA single strand to which the enzyme supposedly bound. Furthermore, the protein could unwind 143-base-pair bluntended duplex DNA at a higher enzyme concentration. It is concluded that RecQ protein is a previously unreported helicase, which might possibly serve to generate single-stranded tails for a strand transfer reaction in the process of recombination.The recQ gene of Escherichia coli (1) is a member of the so-called RecF gene family. The genes ofthis group, the other known members of which are recA, recF, recJ, recN, recO, recR, and ruv (for review, see refs. 2 and 3), share the common denominator that their mutations abolish conjugal recombination proficiency and UV resistance in a mutant lacking active exonuclease V (RecBCD enzyme) and exonuclease I (SbcB protein). In such a mutant, the conjugal recombination system operative in wild-type cells (the RecBCD pathway), which is also implicated in the postreplication recombinational repair of UV-damaged DNA (4), is no longer functional due to the loss of the key enzyme exonuclease V (see ref.2). To explain the conjugal recombination proficiency and UV resistance of the mutant, it is generally assumed that the absence of exonuclease I somehow activates a substitute system, the RecF pathway (5), which is dependent on the RecF family genes (2). In addition to the above assignments, recent work has revealed the roles for the RecF family genes in plasmid recombination (6)(7)(8).

Biochemical and Kinetic Characterization of the DNA Helicase and Exonuclease Activities of Werner Syndrome Protein

“…Mn 2ϩ was also found to serve as a cofactor for Sgs1 helicase (53) and RecQ ATPase (54) reactions. An interesting result was obtained when Zn 2ϩ was used to replace Mg 2ϩ in the WRN enzymatic reaction.…”

Cell cycle regulation of the endogenous wild type Bloom's syndrome DNA helicase

“…The BLM protein has been identi®ed as a member in the DExH boxcontaining RecQ helicase subfamily (Ellis et al, 1995). Its primary sequence presents similarities with all known members in the RecQ subfamily, including Escherichia coli RecQ (Umezu et al, 1990), Saccharomyces cerevisiae Sgs1p (Ganglo et al, 1994;Watt et al, 1995), Schizosaccharomyces pombe Rqh1 (Stewart et al, 1997), Drosophila melanogaster DmBLM (Kusano et al, 1999), human RecQL (Puranam and Blackshear, 1994;Seki et al, 1994), human Wrn, the product of the Werner's syndrome gene (Yu et al, 1996) and the recently identi®ed human RecQ4 and RecQ5 proteins (Kitao et al, 1998). Chester et al (1998) developed a mouse model for the human Bloom's syndrome, and showed that mouse embryos homozygous for a targeted mutation in the murine Bloom's syndrome gene die by embryonic day 13.5, but little is known about function(s) of BLM.…”

Bloom's syndrome gene suppresses premature ageing caused by Sgs1 deficiency in yeast

“…Werner's syndrome (WS) and Rothmund±Thomson syndrome (RTS) are rare, autosomal recessive disorders characterized by premature ageing and a predisposition to neoplasia (Rothmund 1868;Thomson 1936;Cerimele et al 1982;Vennos et al 1992;Vennos & James 1995;Goto 1997). Recently, the genes, BLM, WRN, and RECQL4, responsible for BS, WS and RTS, respectively, have been found to be homologues of Escherichia coli recQ and Saccharomyces cerevisiae SGS1 genes, which encode DNA helicases (Nakayama et al 1984;Umezu et al 1990;Ellis et al 1995;Watt et al 1996;Yu et al 1996;Kitao et al 1999).…”