title: DNA bending, compaction and negative supercoiling by the architectural protein Sso7d of Sulfolobus solfataricus.
abstract: Members of the Sso7d/Sac7d family are small, abundant, non-specific DNA-binding proteins of the hyperthermophilic Archaea SULFOLOBUS: Crystal structures of these proteins in complex with oligonucleotides showed that they induce changes in the helical twist and marked DNA bending. On this basis they have been suggested to play a role in organising chromatin structures in these prokaryotes, which lack histones. We report functional in vitro assays to investigate the effects of the observed Sso7d-induced structural modifications on DNA geometry and topology. We show that binding of multiple Sso7d molecules to short DNA fragments induces significant curvature and reduces the stiffness of the complex. Sso7d induces negative supercoiling of DNA molecules of any topology (relaxed, positively or negatively supercoiled) and in physiological conditions of temperature and template topology. Binding of Sso7d induces compaction of positively supercoiled and relaxed DNA molecules, but not of negatively supercoiled ones. Finally, Sso7d inhibits the positive supercoiling activity of the thermophile-specific enzyme reverse gyrase. The proposed biological relevance of these observations is that these proteins might model the behaviour of DNA in constrained chromatin environments.
authors.affiliation: Institute of Protein Biochemistry and Enzymology, Consiglio Nazionale delle Ricerche, Via Pietro Castellino 111, 80131 Naples, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Napoli
authors.forename: Yvan
authors.initials: Y
authors.lastname: Zivanovic
authors.forename: Chantal
authors.initials: C
authors.lastname: Bocs
authors.forename: Cyril
authors.initials: C
authors.lastname: Buhler
authors.forename: Mose'
authors.initials: M
authors.lastname: Rossi
authors.forename: Patrick
authors.initials: P
authors.lastname: Forterre
authors.forename: Maria
authors.initials: M
authors.lastname: Ciaramella
mesh_terms: D019843:Archaeal Proteins; D026942:DNA Topoisomerases / Q000378:metabolism; D004264:DNA Topoisomerases, Type I; D019641:DNA, Archaeal / Q000737:chemistry* / Q000378:metabolism; D004270:DNA, Circular / Q000737:chemistry; D004278:DNA, Superhelical / Q000737:chemistry*; D004268:DNA-Binding Proteins / Q000378:metabolism* / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D009690:Nucleic Acid Conformation; D016944:Sulfolobus; D059004:Topoisomerase I Inhibitors
chemical_list: D019843:Archaeal Proteins; D019641:DNA, Archaeal; D004270:DNA, Circular; D004278:DNA, Superhelical; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; C093228:Sso7d protein, Sulfolobus; D059004:Topoisomerase I Inhibitors; D026942:DNA Topoisomerases; C041813:DNA reverse gyrase; D004264:DNA Topoisomerases, Type I