RNA DEGRADATION IN ESCHERICHIA-COLI REGULATED BY 3' ADENYLATION AND 5' PHOSPHORYLATIAN

ALTHOUGH polyadenylation 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 I-8, an antisense repressor 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 phosphorylase(9); conversely, mutation of the polynucleotide phosphorylase-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 mRNA-like half-life to RNA I suggests a possible mechanism to account for the rapid decay of mRNA(10) in E. coli.