Catabolite repression signaling in bacteria:

• In bacteria such as E. coli, glucose is the preferred energy metabolite; when glucose is absent or depleted, adenylate cyclase activity increases, producing high levels of cyclic adenosine monophosphate (cAMP) that signals nutrient stress to activate the CAP/CRP activator.
• cGMP is an intracellular second messenger in eukaryotic pathways.
• Inositol phosphates participate in eukaryotic calcium signaling cascades.
• Tyrosine kinases phosphorylate protein tyrosine residues in eukaryotes.

Function of the trp operon:

• The trp operon in E. coli is a repressible operon that encodes five enzymes (TrpE, TrpD, TrpC, TrpB, TrpA) responsible for the anabolic biosynthesis of the essential amino acid tryptophan from chorismate.
• Tryptophan degradation (catabolism) is not mediated by this operon.
• Interconversions are handled by independent enzymes.
• Precursor chorismate synthesis is encoded by the common shikimate pathway genes, not the trp operon.