A purine polyribonucleotide synthetase from Escherichia coli

The isolation, from E. coli B, and partial purification of a purine polyribonucleotide synthetase having several unusual properties is described. The enzyme, which seems to be under strict regulation by several nucleoside triphosphates, requires, after removal of internal primer activity, a primer, such as poly(A), poly(U), or a suitable RNA, but acts without a template. It uses purine ribonucleoside triphosphates as precursors. The uptake of adenylic acid, when ATP is offered alone, is highly stimulated by the presence of GTP, in which case both nucleotides are incorporated into mixed polymers; but GTP as the sole precursor is not utilized. CTP has a strongly inhibitory effect. Other unusual features are the high salt concentration, 0.6 M KCl, at which the enzyme is optimally active and evidence of the existence of a relatively heat-stable protein functioning as an activation factor.