title: The Sso7d DNA-binding protein from Sulfolobus solfataricus has ribonuclease activity.
abstract: Sso7d is a small, basic, abundant protein from the thermoacidophilic archaeon Sulfolobus solfataricus. Previous research has shown that Sso7d can bind double-stranded DNA without sequence specificity by placing its triple-stranded beta-sheet across the minor groove. We previously found RNase activity both in preparations of Sso7d purified from its natural source and in recombinant, purified protein expressed in Escherichia coli. This paper provides conclusive evidence that supports the assignment of RNase activity to Sso7d, shown by the total absence of activity in the single-point mutants E35L and K12L, despite the preservation of their overall structure under the assay conditions. In keeping with our observation that the residues putatively involved in RNase activity and those playing a role in DNA binding are located on different surfaces of the molecule, the activity was not impaired in the presence of DNA. If a small synthetic RNA was used as a substrate, Sso7d attacked both predicted double- and single-stranded RNA stretches, with no evident preference for specific sequences or individual bases. Apparently, the more readily attacked bonds were those intrinsically more unstable.
authors.affiliation: Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Biocca, Milan, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Shehi
authors.forename: S
authors.initials: S
authors.lastname: Serina
authors.forename: G
authors.initials: G
authors.lastname: Fumagalli
authors.forename: M
authors.initials: M
authors.lastname: Vanoni
authors.forename: R
authors.initials: R
authors.lastname: Consonni
authors.forename: L
authors.initials: L
authors.lastname: Zetta
authors.forename: G
authors.initials: G
authors.lastname: Dehò
authors.forename: P
authors.initials: P
authors.lastname: Tortora
authors.forename: P
authors.initials: P
authors.lastname: Fusi
mesh_terms: D019943:Amino Acid Substitution; D019843:Archaeal Proteins / Q000378:metabolism; D002384:Catalysis; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D004795:Enzyme Stability / Q000502:physiology; D004926:Escherichia coli / Q000235:genetics; D006358:Hot Temperature; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D011487:Protein Conformation; D011489:Protein Denaturation / Q000502:physiology; D012358:RNA, Transfer, Met / Q000378:metabolism / Q000494:pharmacology; D012260:Ribonucleases / Q000378:metabolism*; D013379:Substrate Specificity; D016944:Sulfolobus
chemical_list: D019843:Archaeal Proteins; D004268:DNA-Binding Proteins; D012358:RNA, Transfer, Met; C093228:Sso7d protein, Sulfolobus; D012260:Ribonucleases