Staphylococcal nuclease: size and specificity of the active site.

The dissociation constants and standard free energies of complex formation determined with staphylococcal nuclease and a series of 5'-phosphoryloligothymidyl derivatives of increasing chain length suggest that maximum stability is reached with an oligonucleotide containing three nucleotide units. A proposed model of the active site that contains other knowledge of the specificity and the catalytic mechanism of this enzyme postulates the existence of three nonequivalent phosphate binding subsites and a closely related phosphodiester hydrolytic subsite.