The ribosomal L13 leader is a putative RNA regulatory element that was found upstream of the rplM-rpsI genes encoding the ribosomal proteins L13 and S9 in Bacillus subtilis and other Firmicutes. The expression of another ribosomal operon in B. subtilis, infC-rpmI-rplT, is autoregulated by a complex transcription attenuation mechanism involving the formation of alternative structures in the leader mRNA which depends upon the presence of ribosomal protein L20 [17289755]. Similar transcription attenuation mechanism that can be proposed for the L13 leader has not been yet experimentally validated.