S6:S18 ribosomal protein leader is a ribosomal protein leader involved in the ribosome biogenesis. It is used as an autoregulatory mechanism to control the concentration of the ribosomal proteins S6:S18 complex. An experimentally confirmed example of such a leader occurs in a wide variety of bacteria,[1] though not all phyla. A S6:S18 ribosomal leader was predicted in Chlorobia,[2] and its predicted structure differs from that of the validated S6:S18 ribosomal leader. This structure is located in the 5′ untranslated regions of mRNAs encoding ribosomal proteins rpsF (S6), the Single-strand DNA-binding protein A (ssbA), S18 (rpsR) and L7/L12 (rpll).[2]