title: Analysis of the unwinding activity of the dimeric RECQ1 helicase in the presence of human replication protein A.
abstract: RecQ helicases are required for the maintenance of genome stability. Characterization of the substrate specificity and identification of the binding partners of the five human RecQ helicases are essential for understanding their function. In the present study, we have developed an efficient baculovirus expression system that allows us to obtain milligram quantities of recombinant RECQ1. Our gel filtration and dynamic light scattering experiments show that RECQ1 has an apparent molecular mass of 158 kDa and a hydrodynamic radius of 5.4 +/- 0.6 nm, suggesting that RECQ1 forms dimers in solution. The oligomeric state of RECQ1 remains unchanged upon binding to a single-stranded (ss)DNA fragment of 50 nt. We show that RECQ1 alone is able to unwind short DNA duplexes (<110 bp), whereas considerably longer substrates (501 bp) can be unwound only in the presence of human replication protein A (hRPA). The same experiments with Escherichia coli SSB show that RECQ1 is specifically stimulated by hRPA. However, hRPA does not affect the ssDNA-dependent ATPase activity of RECQ1. In addition, our far western, ELISA and co-immunoprecipitation experiments demonstrate that RECQ1 physically interacts with the 70 kDa subunit of hRPA and that this interaction is not mediated by DNA.
authors.affiliation: International Centre for Genetic Engineering and Biotechnology, Padriciano 99, I-34012 Trieste, Italy.
authors.forename: Sheng
authors.initials: S
authors.lastname: Cui
authors.forename: Daniele
authors.initials: D
authors.lastname: Arosio
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Doherty
authors.forename: Robert M
authors.initials: RM
authors.lastname: Brosh
authors.forename: Arturo
authors.initials: A
authors.lastname: Falaschi
authors.forename: Alessandro
authors.initials: A
authors.lastname: Vindigni
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D026481:Blotting, Far-Western; D002850:Chromatography, Gel; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004265:DNA Helicases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D019281:Dimerization; D004797:Enzyme-Linked Immunosorbent Assay; D006367:HeLa Cells; D006801:Humans; D011233:Precipitin Tests; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D053484:RecQ Helicases; D051716:Replication Protein A; D012542:Scattering, Radiation
chemical_list: D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; C497167:RPA1 protein, human; D051716:Replication Protein A; D000255:Adenosine Triphosphate; D004247:DNA; D000251:Adenosine Triphosphatases; C506731:RECQL4 protein, human; D004265:DNA Helicases; D053484:RecQ Helicases