Oligoribonuclease is distinct from the other known exoribonucleases of Escherichia coli

Oligoribonuclease, an exoribonuclease specific for small oligoribonucleotides, was initially characterized 20 years ago (S. K. Niyogi and A. K. Datta, J. Biol. Chem. 250:7307-7312, 1975) and shown to be different from RNase II and polynucleotide phosphorylase. Here we demonstrate, using mutant strains and purified enzymes, that oligoribonuclease is not a manifestation of RNases D, BN, T, PH, and R, exoribonucleases discovered subsequently. Thus, oligoribonuclease is the eighth distinct exoribonuclease discovered in Escherichia coli. We also show that oligoribonuclease copurifies with polynucleotide phosphorylase.