Tryptophan operon is primarily involved in
trp operon governs anabolism, construction of complex amino acid molecule from simpler precursors. Chorismate derived from shikimate pathway is converted through anthranilate, phosphoribosyl anthranilate, carboxyphenylamino deoxyribulose phosphate, and indole-3-glycerol phosphate intermediates to final L-tryptophan via enzymes encoded by trpE trpD trpC trpB trpA. Cell undertakes costly reactions consuming ATP, phosphoribosyl pyrophosphate, and glutamine amide donor. When tryptophan abundantly available in environment, cell conserves resources and energy by repressing biosynthetic enzyme synthesis. Catabolic operons like lac instead break down substrates for energy, so their regulatory logic favors induction by available substrate rather than repression by product accumulation.
Ref: NCBI Bookshelf Transcription in Prokaryotes – trp operon encodes anabolic enzymes for tryptophan biosynthesis from chorismate.