15 Ribonuclease III

Abstract

Ribonuclease III (RNase III) of Escherichia coli is responsible for the first steps in the post-transcriptional processing of E. coli ribosomal RNA. RNase III was first characterized as an endoribonuclease that specifically degrades double-stranded RNAs of either natural or synthetic origin. Double-stranded RNA is an effective competitive inhibitor of RNase III cleavage at processing sites, suggesting that specific cleavage sites in single-stranded RNAs may have some double-stranded character. Enzymatic activities that degrade double-stranded RNA have been identified in a variety of eukaryotic tissues, and some of these enzymes may play roles in the processing of precursor RNAs. This chapter focuses on RNase III of E. coli , which is the most extensively studied RNase. Double-stranded RNase activity is usually monitored during the enzymes purification. RNase III cleavage of double-stranded RNA is generally characterized with regard to the type of end groups produced and the size of the products. Exhaustive RNase III digestion of double-stranded RNA produces a mixture of oligonucleotides having 5'-phosphate and 3'-hydroxyl termini.