title: Single molecule force spectroscopy of salt-dependent bacteriophage T7 gene 2.5 protein binding to single-stranded DNA.
abstract: The gene 2.5 protein (gp2.5) encoded by bacteriophage T7 binds preferentially to single-stranded DNA. This property is essential for its role in DNA replication and recombination in the phage-infected cell. gp2.5 lowers the phage lambda DNA melting force as measured by single molecule force spectroscopy. T7 gp2.5-Delta26C, lacking 26 acidic C-terminal residues, also reduces the melting force but at considerably lower concentrations. The equilibrium binding constants of these proteins to single-stranded DNA (ssDNA) as a function of salt concentration have been determined, and we found for example that gp2.5 binds with an affinity of (3.5 +/- 0.6) x 10(5) m(-1) in a 50 mm Na(+) solution, whereas the truncated protein binds to ssDNA with a much higher affinity of (7.8 +/- 0.9) x 10(7) m(-1) under the same solution conditions. T7 gp2.5-Delta26C binding to single-stranded DNA also exhibits a stronger salt dependence than the full-length protein. The data are consistent with a model in which a dimeric gp2.5 must dissociate prior to binding to ssDNA, a dissociation that consists of a weak non-electrostatic and a strong electrostatic component.
authors.affiliation: Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, 111 Dana Research Center, Boston, MA 02115, USA.
authors.forename: Leila
authors.initials: L
authors.lastname: Shokri
authors.forename: Boriana
authors.initials: B
authors.lastname: Marintcheva
authors.forename: Charles C
authors.initials: CC
authors.lastname: Richardson
authors.forename: Ioulia
authors.initials: I
authors.lastname: Rouzina
authors.forename: Mark C
authors.initials: MC
authors.lastname: Williams
mesh_terms: D017123:Bacteriophage T7 / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism*; D011485:Protein Binding; D012492:Salts; D014764:Viral Proteins / Q000378:metabolism*
chemical_list: D004277:DNA, Single-Stranded; D012492:Salts; D014764:Viral Proteins