Interaction of the HB protein of Bacillus globigii with nucleic acids

Abstract

Fluorescence of the phenylalanine residues of the HB protein of B. globigii was quenched upon binding to nucleic acids. Using this phenomenon, the binding properties were investigated on the basis of an approach published recently. The stoichiometric numbers were .apprx. 10 base pairs/bound protein molecule for double-stranded DNA and .apprx. 10 bases for single-stranded polynucleotides, independent of salt concentration. Cooperativity parameters were in the range of 50-250. Binding constants were .apprx. 5 .times. 106 M-1 (at 0.1 M NaCl) and decreased with increasing salt concentration. From the salt dependence it is inferred that .apprx. 1 Na+ is displaced upon binding of a protein molecule to DNA. The binding site should contain 1 positively charged amino acid residue. The protein binds with comparable strength to double-stranded and single-stranded DNA and to poly(rA). The HB protein does not belong to the category of melting proteins.