[Barnase mutant Ser57Ala: preparation and properties]

Barnase, an extracellular ribonuclease produced by Bacillus amyloliquefaciens, belongs to a family of small microbial ribonucleases with similar structure and properties. These enzymes hydrolyze phosphodiester bonds on the 3' side of guanosine nucleotides in RNA. The guanylic specificity of barnase is more pronounced in the hydrolysis of dinucleotides or cyclonucleotide phosphates as substrates than in the hydrolysis of RNA or polynucleotides. To have an insight into the molecular basis of this phenomenon, we mutated amino acid residue Ser-57 in the "base recognition loop" of RNase Ba. The mutant protein was expressed in Escherichia coli producing system and purified for the study of the kinetic properties in the cleavage polynucleotide reactions. It was shown that the mutation of amino acid residue Ser-57 for Ala in the "recognition loop" of RNase Ba does not significantly influence the kinetic parametres of hydrolysis of polynucleotide substrates.