RNA degradation in Escherichia coli regulated by 3' adenylation and 5' phosphorylation

Abstract

ALTHOUGH polv adenylation has commonly been regarded as a special feature of eukaryotic messenger RNA^1,2, there are many reports of polyA tails on bacterial RNA (for example, refs 3–8). In Escherichia coli, adenylation mediated by the pcnB gene greatly accelerates decay of RNA I⁸, an antisense represser of replication of ColE1 type plasmids that resembles highly structured transfer RNA but shows the rapid turnover characteristic of mRNA. Here we report that both 3' adenylation and 5' phosphorylation affect the rate of digestion of RNA I by the 3' exonuclease, polynucleotide phosphorylase⁹; conversely, mutation of the polynucleotide phos-phorylase-encoding pnp gene affects ribonuclease acting at the 5' end. Together these findings indicate that enzymes attacking RNA I at its separate termini can interact functionally. Additionally, our discovery that adenylation-mediated degradation by polynucleotide phosphorylase imparts an mRN A-Iike half-life to RNA I suggests a possible mechanism to account for the rapid decay of mRNA¹⁰ in E. coli.