Final answer:
Charles Yanofsky discovered that the trp operon is a negatively regulated cluster of genes where the presence of tryptophan activates a repressor protein, which then inhibits the operon's transcription, demonstrating feedback inhibition.
Step-by-step explanation:
Charles Yanofsky's research on the trp operon led to the discovery of an important mechanism of gene regulation in bacteria. The trp operon is a cluster of genes involved in the synthesis of the amino acid tryptophan in Escherichia coli. In the absence of tryptophan, the corresponding repressor protein is inactive and does not bind to the operator, allowing RNA polymerase to transcribe the genes needed to synthesize tryptophan. This is considered a negatively regulated operon, as it is active when a repressor is not bound to the operator.
However, when tryptophan levels are sufficient, it binds to the repressor making it active, which then binds to the operator and prevents transcription of the operon. Hence, Charles Yanofsky helped to elucidate the concept of feedback inhibition, where the end product of a metabolic pathway can regulate its own production by inhibiting gene expression through a repressor protein.