An allosteric transcription regulator called HisP regulates the enzymes for hist

Question

An allosteric transcription regulator called HisP regulates the enzymes for histidine biosynthesis in the bacterium E coil. 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. Compare/contrast the regulatory sequences HisP would bind if it functions as a gene repressor versus a gene activator 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 As on 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

Explanation / Answer

a. Regulation of gene expression: - In DNA regulation of gene expression occurs at the level of RNA biosynthesis or transcription. This is accomplished by binding of transcription factors to specific sequence which brings about activation or inhibition of transcription. Thus transcription factors can act as activator or repressors or both.

b. A regulatory sequence is a segment of DNA capable of increasing or decreasing the expression of specific genes in an organism.

HisP functions as a gene repressor when histidine is present in abundance. It would bind more tightly to the regulatory sequences and less tightly to the promoter sequence so that the transcription of genes of histidine biosynthetic pathway is turned off. The operon is thus “turned off”. This ensures that there is no overproduction of histidine.

c. When histidine levels are low, HisP functions as an activator. It would bind less tightly to the regulatory sequences and more tightly to the promoter sequence so that the transcription of genes of histidine biosynthetic pathway is turned on. The operon is thus “turned on”.

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