Figure 2. The Escherichia coli RNA degradosome, and facilitated substrate delivery to the exoribonuclease component, polynucleotide phosphorylase (PNPase, blue). A portion of the PNPase ring has been removed to illustrate the central chamber that harbors the active site. An ATP-dependent DEAD box helicase RhlB (green), another degradosome component, is unwinding the RNA stem-loop (red), providing a single-stranded RNA for PNPase. Both enzymes are associated with RNase E (purple). For clarity, other degradosome components, such as enolase, were omitted.