Deletion of both gives upto 20-fold depletion in the ability of LacI to block transcription. Amino acid Biosynthesis. Each of these genes encode for an isozyme which is involved in the synthesis of all three of the aromatic amino acids in E. coli . Essentially a means to modify transcriptional termination by providing options to the termination stem-loop structure followed by the sequence of poly U's. Curious relationship of tryptophan codons to the first stem loop structures.
Attenuation is a cis acting regulatory control.
Role of variable formation of secondary structures in the controlled transcriptional expression of downstream genes.