Journal of Bacteriology, May 2000, p. 2468-2475, Vol. 182, No. 9
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Skirball Institute of Biomolecular Medicine and Department of Microbiology, New York University School of Medicine, New York, New York 10016
Received 17 December 1999/Accepted 18 February 2000
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.
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