An allosteric transcription regulator called HisP regulates the enzymes for histidine biosynthesis in the bacterium E. coli. Histidine modulates HisP activity. On binding histidine, HisP alters its conformation, markedly changing its affinity for the regulatory sequences in the promoters of the genes for the histidine biosynthetic enzymes. a. Compare/contrast the regulatory sequences HisP would bind if it functions as a gene repressor verus a gene activator.
b. As a repressor, would you expect that HisP would bind more tightly or less tightly to the regulatory sequences when histidine is abundant? Explain your answer.
c. As an activator, would you expect that HisP would bind more tightly or less tightly to the regulatory sequences when histidine levels are low? Explain your answer.