title: Characterization of the Pf3 single-strand DNA binding protein by circular dichroism spectroscopy.
abstract: We have used circular dichroism (CD) spectroscopy and gel electrophoresis to characterize the single-strand DNA binding protein (ssDBP) of the bacteriophage Pf3 and its complexes with Pf3 DNA and various DNA and RNA homopolymers. The secondary structure of Pf3 ssDBP had < 1% alpha-helix and therefore was probably a beta-sheet structure like the fd gene 5 protein (g5p). From CD titrations, the binding stoichiometry of Pf3 ssDBP was two nucleotides per protein monomer (n = 2) for complexes formed with all of the nucleic acids except poly[r(U)], for which n = 3 (in a buffer of 10 mM Tris-HCl and 70 mM NaCl, pH 8.2). Evidence of an additional binding mode of n = 4 for complexes formed with Pf3 DNA was found by gel electrophoresis experiments. Pf3 ssDBP showed a marked sequence dependence in binding affinities similar to that known for the fd g5p.
authors.affiliation: Program in Molecular and Cell Biology, University of Texas at Dallas 75083-0688.
authors.forename: M D
authors.initials: MD
authors.lastname: Powell
authors.forename: D M
authors.initials: DM
authors.lastname: Gray
mesh_terms: D001435:Bacteriophages / Q000737:chemistry*; D001483:Base Sequence; D002942:Circular Dichroism; D004277:DNA, Single-Stranded / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000648:ultrastructure*; D003852:Deoxyribonucleoproteins / Q000737:chemistry; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D017433:Protein Structure, Secondary; D011550:Pseudomonas aeruginosa
chemical_list: D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D003852:Deoxyribonucleoproteins; D009838:Oligodeoxyribonucleotides