The Escherichia coli RNA degradosome: structure, function and relationship to other ribonucleolytic multienyzme complexes

mRNA instability is an intrinsic property that permits timely changes in gene expression by limiting the lifetime of a transcript. The RNase E of Escherichia coli is a single-strand-specific endonuclease involved in the processing of rRNA and the degradation of mRNA. A nucleolytic multienzyme complex now known as the RNA degradosome was discovered during the purification and characterization of RNase E. Two other components are a 3′ exoribonuclease (polynucleotide phosphorylase, PNPase) and a DEAD-box RNA helicase (RNA helicase B, RhlB). RNase E is a large multidomain protein with N-terminal ribonucleolytic activity, an RNA-binding domain and a C-terminal ‘scaffold’ that binds PNPase, enolase and RhlB. RhlB by itself has little activity but is strongly stimulated by its interaction with RNase E. RhlB in vitro can facilitate the degradation of structured RNA by PNPase. Since the discovery of the RNA degradosome in E. coli, related complexes have been described in other organisms.