The mechanism of DNA translocation by papillomavirus E1 and polyomavirus LTag hexameric helicases involves consecutive remodelling of subunit-subunit interactions around the hexameric ring. Our biochemical analysis of E1 helicase demonstrates that a 26-residue C-terminal segment is critical for maintaining the hexameric assembly. As this segment was not resolved in previous crystallographic ana...

RecG is a DNA translocase encoded by most species of bacteria. The Escherichia coli protein targets branched DNA substrates and drives the unwinding and rewinding of DNA strands. Its ability to remodel replication forks and to genetically interact with PriA protein have led to the idea that it plays an important role in securing faithful genome duplication. Here we report that RecG co-localises...

In both eukaryotic and prokaryotic DNA sequences of 30–100 base-pairs rich in AT base-pairs have been identified at which the double helix preferentially unwinds. Such DNA unwinding elements are commonly associated with origins for DNA replication and transcription, and with chromosomal matrix attachment regions. Here we present a quantitative study of local DNA unwinding based on extensive sin...

A specific complex is formed between fd DNA, Escherichia coli DNA unwinding protein, and RNA polymerase (EC 2.7.7.6; nucleosidetriphosphate:RNA nucleotidyltransferase) during the first steps in the conversion of the single-stranded viral DNA to the double-stranded replicative form. In this complex a unique DNA fragment of about 120 nucleotides is protected against nuclease digestion. Both the r...

The RecQ helicases belong to an important family of highly conserved DNA helicases that play a key role in chromosomal maintenance, and their defects have been shown to lead to several disorders and cancer in humans. In this work, the conformational and functional properties of the Escherichia coli RecQ helicase have been determined using a wide array of biochemical and biophysical techniques. ...

Recently the gene encoding a member of the RecQ helicase family, RecQ5, was cloned from the fruit fly, Drosophila melanogaster [J.J.Sekelsky, M.H.Brodsky, G.M. Rubin and R.S. Hawley (1999) Nucleic Acids Res., 27, 3762-3769]. The Drosophila RecQ5 transcript is alternatively spliced, like its human counterpart, to yield three protein isoforms. Two of these isoforms are almost identical and have a...

The oligomeric state of Superfamily I DNA helicases is the subject of considerable and ongoing debate. While models based on crystal structures imply that a single helicase core domain is sufficient for DNA unwinding activity, biochemical data from several related enzymes suggest that a higher order oligomeric species is required. In this work we characterize the helicase activity of the AddAB ...

The RNA-guided CRISPR-Cas9 nuclease has revolutionized genome engineering, yet its mechanism for DNA target selection is not fully understood. A crucial step in Cas9 target recognition involves unwinding of the DNA duplex to form a three-stranded R-loop structure. Work reported here demonstrates direct detection of Cas9-mediated DNA unwinding by a combination of site-directed spin labeling and ...

Immune dysfunction is linked with lymphocyte DNA metabolism. In particular, DNA damage may impair lymphocyte function and induce increased cell turnover; such changes are of relevance to the pathogenesis of rheumatoid arthritis. The rate of DNA unwinding in alkaline solution was used as a measure of the number of DNA strand breaks in mononuclear cells freshly isolated from peripheral blood. The...

A novel ATP-dependent DNA unwinding enzyme, called human DNA helicase VI (HDH VI), was purified to apparent homogeneity from HeLa cells and characterized. From 327 g of cultured cells, 0.44 mg of pure enzyme was recovered, free of DNA polymerase, ligase, topoisomerase, nicking and nuclease activities. The enzyme behaves as a monomer having an M(r) of 128 kDa, whether determined with SDS-PAGE, o...