Bacterial mRNAs begin with a triphosphate on the first transcribed nucleotide, but RNase E, the endonuclease long thought to initiate mRNA decay in Escherichia coli, only works well on RNA with a 5′-monophosphate. Conversion of the 5′-triphosphate to a monophosphate now appears to be the first committed step in mRNA decay in E. coli.
