Polyguanylic acid-inhibited ribonuclease of Klebsiella: II. Studies with synthetic polyribonucleotides

Abstract

Purified Klebsiella ribonuclease (ribonucleate nucleotido-2′-transferase (cyclizing), EC 2.7.7.17) is able to hydrolyze poly(A), poly(U) and poly(C) more readily than yeast RNA, but cannot attack poly(G), poly(I), poly(X), poly(hU), poly(A) · poly(U) and poly(I) · poly(C). Hydrolysis of yeast RNA, poly(U), and poly(A) by this nuclease is inhibited markedly by poly(G) and to a much lesser extent by poly(I). Another compound, poly(X), is more potent than poly(I) as an inhibitor of RNA hydrolysis but less potent in inhibiting poly(U) hydrolysis. Relatively high concentrations of poly(hU) will inhibit poly(U) hydrolysis but have no effect when yeast RNA is the substrate. A number of mononucleotides were tested and have no effect on RNA hydrolysis by Klebsiella nuclease. Several other nucleases were found to be inhibited to a greater or lesser extent by poly(G) and poly(I). The data suggest that the nuclease prefers molecules of unordered secondary structure as substrates, and that ordered molecules are not attacked and may actually be inhibitors.