A DEAD-box RNA helicase in the Escherichia coli RNA degradosome

THE Escherichia coli RNA degradosome is a multi-enzyme complex that contains the exoribonuclease polynucleotide phosphorylase (PNPase) and the endoribonuclease RNase E 1,2 . Both enzymes are important in RNA processing and messenger RNA degradation 3–14 . Here we report that enolase and RhlB are two other major components of the degradosome. Enolase is a glycolytic enzyme with an unknown role in RNA metabolism. RhlB is a member of the DEAD-box family of ATP-dependent RNA helicases, which are found in both prokaryotes and eukaryotes 15–26 . We show that the degradosome has an ATP-dependent activity that aids the degradation of structured RNA by PNPase. Incubation of the degradosome with affinity-purified antibody against RhlB inhibited the ATP-stimulated RNA degradation. These results suggest that RhlB acts by unwinding RNA structures that impede the processive activity of PNPase. RhlB is thus an important enzyme in mRNA turnover.