The RNA degradosome: life in the fast lane of adaptive molecular evolution

In Escherichia coli, the multi-enzyme RNA degradosome contributes to the global, posttranscriptional regulation of gene expression. The degradosome components are recognized through natively unstructured ‘microdomains’ comprising as few as 15–40 amino acids. Consequently, the degradosome might experience a comparatively smaller number of evolutionary constraints, because there is little requirement to maintain a folded state for the interaction sites. New regulatory properties of the degradosome could arise with relative rapidity, because partners that modify its function could be recruited by quickly evolving microdomains. The unusual combination of the centrality of RNA degradation in gene expression and the generality of natively unstructured microdomains in recognition can fortuitously confer a capacity for efficacious adaptive change to degradosome-like assemblies in eubacteria.