The Small Protein cS24 Encoded by Gene ssr3189 is an RNA-Binding Ribosomal Protein Specific for Cyanobacteria that Is Involved in Metabolic Regulation

Deletion of ssr3189 resulted in lower pigmentation, delayed growth, and alterations in the expression of genes encoding transporters for nitrogen and Ci, and metabolic enzymes. Metabolomic analysis revealed a substantial overaccumulation of glutamine and tricarboxylic acid (TCA) cycle intermediates in the deletion mutant, and further differences in the amino acid and organic acid pools compared to the wild type. Co-immunoprecipitation with a strain expressing C-terminally tagged cS24 yielded ribosomal protein S21, enolase and the Cas6-1 endoribonuclease as the most strongly co-enriched proteins, consistent with the involvement with ribosomes and pointing at further functions.