A number of bacterial biosynthetic operons have been examined in Escherichia coli and Salmonella typhimurium, many of which show attenuation very similar to that seen in the tryptophan system in E. coli. Below are partial amino acid sequences of leader peptides. For each, predict the amino acid that is likely to be synthesized by the operon for each attenuator element. Explain your reasoning. For leader peptide C, how would changing the histidine codons to alanine codons effect the regulation of the operon?

A. Met-Ser-His-Ile-Val-Arg-Phe-Thr-Gly-Leu-Leu-Leu-Leu-Asn-Ala-Phe-Ile-Val-Arg—
B. Met-Lys-Arg-Ile-Ser-Thr-Thr-Ile-Thr-Thr-Thr-Ile-Thr-Ile-Thr-Thr-Gly-Asn-Gly-Ala—
C. Met-Thr-Arg-Val-Gln-Phe-Lys-His-His-His-His-His-His-His-Pro-Asp—
D. Met-Lys-His-Ile-Pro-Phe-Phe-Phe-Ala-Phe-Phe-Phe-Thr-Phe-Pro—