A Novel RNA Phosphorylation State Enables 5′ End-Dependent Degradation in Escherichia coli

5 years ago

A Novel RNA Phosphorylation State Enables 5′ End-Dependent Degradation in Escherichia coli

RNA modifications that once escaped detection are now thought to be pivotal for governing RNA lifetimes in both prokaryotes and eukaryotes. For example, converting the 5′-terminal triphosphate of bacterial transcripts to a monophosphate triggers 5′ end-dependent degradation by RNase E. However, the existence of diphosphorylated RNA in bacteria has never been reported, and no biological role for such a modification has ever been proposed. By using a novel assay, we show here for representative Escherichia coli mRNAs that ∼35%–50% of each transcript is diphosphorylated. The remainder is primarily monophosphorylated, with surprisingly little triphosphorylated RNA evident. Furthermore, diphosphorylated RNA is the preferred substrate of the RNA pyrophosphohydrolase RppH, whose biological function was previously assumed to be pyrophosphate removal from triphosphorylated transcripts. We conclude that triphosphate-to-monophosphate conversion to induce 5′ end-dependent RNA degradation is a two-step process in E. coli involving γ-phosphate removal by an unidentified enzyme to enable subsequent β-phosphate removal by RppH.

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Luciano et al. show that diphosphorylated mRNA 5′ ends are abundant in E. coli and that the E. coli RNA pyrophosphohydrolase RppH prefers diphosphorylated substrates to their triphosphorylated counterparts. Their findings suggest that converting triphosphorylated to monophosphorylated 5′ ends before RNase E cleavage involves sequential phosphate removal by distinct enzymes.

Publisher URL: www.sciencedirect.com/science

DOI: S1097276517303994