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Himabindu, P. and Anupama, K. (2017) Decreased expression of stable RNA can alleviate the lethality associated with RNase E deficiency in Escherichia coli. Journal of Bacteriology, 199 (8). e00724-16. ISSN 0021-9193

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The endoribonuclease RNase E participates in mRNA degradation, rRNA processing and tRNA maturation in Escherichia coli, but the precise reasons for its essentiality are unclear and much debated. The enzyme is most active on RNA substrates with a 5' -terminal monophosphate, which is sensed by a domain in the enzyme that includes residue R169; E. coli also possesses a 5' -pyrophosphohydrolase RppH that catalyses conversion of 5' -terminal-triphosphate to -monophosphate on RNAs. Although the C-terminal half (CTH), beyond residue approximately 500, of RNase E is dispensable for viability, the ΔCTH mutation is lethal when combined with an R169Q mutation or with deletion of rppH In this work, we show that both these lethalities can be rescued in derivatives in which four, or five, of the seven rrn operons in the genome have been deleted. We hypothesise that the reduced stable RNA levels under these conditions minimizes the need of RNase E to process them, thereby allowing for its diversion for mRNA degradation. In support of this hypothesis, we have found that other conditions that are known to reduce stable RNA levels also suppress one or both lethalities: (i) alterations in relA and spoT that are expected to lead to increased basal ppGpp levels; (ii) stringent rpoB mutations which mimic high intracellular ppGpp levels; and (iii) overexpression of DksA. Lethality suppression by these perturbations was RNase R-dependent. Our work therefore suggests that its actions on the various substrates (mRNA, rRNA, and tRNA) jointly contribute to the essentiality of RNase E in E. coli IMPORTANCE: The endoribonuclease RNase E is essential for viability in many Gram-negative bacteria, including Escherichia coli Different explanations have been offered for its essentiality, including its roles in global mRNA degradation or in the processing of several tRNA and rRNA species. Our work suggests that, rather than its role in the processing of any one particular substrate, its distributed functions on all the different substrates (mRNA, rRNA and tRNA) is responsible for the essentiality of RNase E in E. coli.

Item Type: Article
Depositing User: Dr P Divakar
Date Deposited: 17 Feb 2017 05:39
Last Modified: 21 Dec 2018 08:48
URI: http://cdfd.sciencecentral.in/id/eprint/770

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