An RNA Pyrophosphohydrolase Triggers 5′-Exonucleolytic Degradation of mRNA in Bacillus subtilis

SummaryIn Escherichia coli, RNA degradation often begins with conversion of the 5′-terminal triphosphate to a monophosphate, creating a better substrate for internal cleavage by RNase E. Remarkably, no homolog of this key endonuclease is present in many bacterial species, such as Bacillus subtilis and various pathogens. Here, we report that the degradation of primary transcripts in B. subtilis can nevertheless be triggered by an analogous process to generate a short-lived, monophosphorylated intermediate. Like its E. coli counterpart, the B. subtilis RNA pyrophosphohydrolase that catalyzes this event is a Nudix protein that prefers unpaired 5′ ends. However, in B. subtilis, this modification exposes transcripts to rapid 5′ exonucleolytic degradation by RNase J, which is absent in E. coli but present in most bacteria lacking RNase E. This pathway, which closely resembles the mechanism by which deadenylated mRNA is degraded in eukaryotic cells, explains the stabilizing influence of 5′-terminal stem-loops in such bacteria.

Graphical AbstractFigure optionsDownload high-quality image (40 K)Download as PowerPoint slideHighlights▸ In Bacillus subtilis, 5′ end-dependent RNA degradation is triggered by RppH ▸ RppH converts the 5′-terminal triphosphate of RNA to a monophosphate ▸ The resulting intermediate is degraded by the 5′ exonuclease activity of RNase J ▸ This pathway explains the protective effect of 5′-terminal stem-loops in B. subtilis