Regions of RNase E important for 5'-end-dependent RNA cleavage and autoregulated synthesis.

RNase E is an important regulatory enzyme that plays a key role in RNA processing and degradation in Escherichia coli. Internal cleavage by this endonuclease is accelerated by the presence of a monophosphate at the RNA 5' end. Here we show that the preference of E. coli RNase E for 5'-monophosphorylated substrates is an intrinsic property of the catalytically active amino-terminal half of the enzyme and does not require the carboxy-terminal region. This property is shared by the related E. coli ribonuclease CafA (RNase G) and by a cyanobacterial RNase E homolog derived from Synechocystis, indicating that the 5'-end dependence of RNase E is a general characteristic of members of this ribonuclease family, including those from evolutionarily distant species. Although it is dispensable for 5'-end-dependent RNA cleavage, the carboxy-terminal half of RNase E significantly enhances the ability of this ribonuclease to autoregulate its synthesis in E. coli. Despite similarities in amino acid sequence and substrate specificity, CafA is unable to replace RNase E in sustaining E. coli cell growth or in regulating RNase E production, even when overproduced sixfold relative to wild-type RNase E levels.