Purification and some novel properties of Escherichia coli RNase II

RNase II of Escherichia coli (EC 3.1.4.23) has been purified to apparent homogeneity. The K+-activated diesterase activity against poly(U), which defines RNase II, cochromatographs with activity against T4 mRNA or pulse-labeled E. coli RNA successively on DEAE-cellulose, hydroxyapatite or phosphocellulose, and Sephadex G-150 columns. Activities with both substrates are selectively reduced to less than 2% of the wild type level in a newly isolated mutant strain, S296, or after thermal inactivation in a mutant strain with temperature-sensitive RNase II. RNase II releases 5'-XMP without a lag as its only detectable alcohol-soluble produce from all substrates and has an apparent molecular weight of 80,000 to 90,000 in both nondissociating and sodium dodecyl sulfate-polyacrylamide gels. The pure enzyme shows the standard K+ activation against poly(A), poly(U), or poly(C), but only a slight preference for K+ over Na+ ions with T4 mRNA or pulse labeled E. coli RNA as substrate. Uniformly labeled E. coli rRNA or tRNA is degraded little if at all.