This family consists of the tryptophanase (tna) operon leader peptide. Tna catalyzes the degradation of L-tryptophan to indole, pyruvate and ammonia, enabling the bacteria to utilize tryptophan as a source of carbon, nitrogen and energy. The tna operon of E. coli contains two major structural genes, tnaA and tnaB. Preceding tnaA in the tna operon is a 319 -nucleotide transcribed regulatory region that contains the coding region for a 24-residue leader peptide, TnaC. The RNA sequence in the vicinity of the tnaC stop codon is rich in Cytidylate residues which is required for efficient Rho -dependent termination in the leader region of the tna operon.