The proteolytic conversion of polynucleotide phosphorylase to a primer-dependent form.

Polynucleotide phosphorylase from Micrococcus luteus (formerly Micrococcus lysodeikticw) can be converted from a primer-independent form (Form-I) to a primer-dependent form (Form-T) by limited proteolysis with trypsin. The conversion of Form-I to Form-T is accompanied by the breaking of between five and six peptide bonds per molecule of enzyme, and results in the removal of a small portion of the peptide chain of each subunit. The two enzymes have molecular weights of 2.6 X lo5 and 2.2 X 106, respectively, and both are composed of four subunits. Restoration of primer independence to Form-T is obtained by treatment of Form-T with sulfhydryl reagents. After thiol treatment, one or two enzyme sulfhydryl groups become titratable.