title: Characterization of the single stranded DNA binding protein SsbB encoded in the Gonoccocal Genetic Island.
abstract: BACKGROUND
  Most strains of Neisseria gonorrhoeae carry a Gonococcal Genetic Island which encodes a type IV secretion system involved in the secretion of ssDNA. We characterize the GGI-encoded ssDNA binding protein, SsbB. Close homologs of SsbB are located within a conserved genetic cluster found in genetic islands of different proteobacteria. This cluster encodes DNA-processing enzymes such as the ParA and ParB partitioning proteins, the TopB topoisomerase, and four conserved hypothetical proteins. The SsbB homologs found in these clusters form a family separated from other ssDNA binding proteins.
  
  
  RESULTS
  In contrast to most other SSBs, SsbB did not complement the Escherichia coli ssb deletion mutant. Purified SsbB forms a stable tetramer. Electrophoretic mobility shift assays and fluorescence titration assays, as well as atomic force microscopy demonstrate that SsbB binds ssDNA specifically with high affinity. SsbB binds single-stranded DNA with minimal binding frames for one or two SsbB tetramers of 15 and 70 nucleotides. The binding mode was independent of increasing Mg(2+) or NaCl concentrations. No role of SsbB in ssDNA secretion or DNA uptake could be identified, but SsbB strongly stimulated Topoisomerase I activity.
  
  
  CONCLUSIONS
  We propose that these novel SsbBs play an unknown role in the maintenance of genetic islands.
authors.affiliation: Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands.
authors.forename: Samta
authors.initials: S
authors.lastname: Jain
authors.forename: Maria
authors.initials: M
authors.lastname: Zweig
authors.forename: Eveline
authors.initials: E
authors.lastname: Peeters
authors.forename: Katja
authors.initials: K
authors.lastname: Siewering
authors.forename: Kathleen T
authors.initials: KT
authors.lastname: Hackett
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Dillard
authors.forename: Chris
authors.initials: C
authors.lastname: van der Does
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D001665:Binding Sites; D004264:DNA Topoisomerases, Type I / Q000737:chemistry; D004269:DNA, Bacterial / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D024202:Electrophoretic Mobility Shift Assay; D015964:Gene Expression Regulation, Bacterial; D044404:Genomic Islands; D008274:Magnesium / Q000737:chemistry; D005810:Multigene Family; D009344:Neisseria gonorrhoeae / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012965:Sodium Chloride / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D011994:Recombinant Proteins; D012965:Sodium Chloride; D004264:DNA Topoisomerases, Type I; D008274:Magnesium