RNA degradosomes exist in vivo in Escherichia coli as multicomponent complexes associated with the cytoplasmic membrane via the N-terminal region of ribonuclease E

RNase E isolated from Escherichia coil is contained in a multicomponent "de gradosome" complex with other proteins implicated in RNA decay. Earlier wor k has shown that the C-terminal region of RNase E is a scaffold for the bin ding of degradosome components and has identified specific RNase E segments necessary for its interaction with polynucleotide phosphorylase (PNPase), RhlB RNA helicase, and enolase. Here, we report electron microscopy studies that use immunogold labeling and freeze-fracture methods to show that degr adosomes exist in vivo in E. coli as multicomponent structures that associa te with the cytoplasmic membrane via the N-terminal region of RNase E. Wher eas PNPase and enolase are present in E, coil in large excess relative to R Nase E and therefore are detected in cells largely as molecules unlinked to the RNase E scaffold, immunogold labeling and biochemical analyses show th at helicase is present in approximately equimolar amounts to RNase E at all cell growth stages. Our findings, which establish the existence and cellul ar location of RNase E-based degradosomes in vivo in E. coil, also suggest that RNA processing and decay may occur at specific sites within cells.