Role of Inorganic Polyphosphate in Promoting Ribosomal Protein Degradation by the Lon Protease in E. coli

Inorganic polyphosphate (polyP), a polymer of hundreds of phosphate (P i ) residues, accumulates in Escherichia coli in response to stresses, including amino acid starvation. Here we show that the adenosine 5′-triphosphate–dependent protease Lon formed a complex with polyP and degraded most of the ribosomal proteins, including S2, L9, and L13. Purified S2 also bound to polyP and formed a complex with Lon in the presence of polyP. Thus, polyP may promote ribosomal protein degradation by the Lon protease, thereby supplying the amino acids needed to respond to starvation.