In the bacterium Salmonella typhimurium, seven of the genes coding for histidine

Question

In the bacterium Salmonella typhimurium, seven of the genes coding for histidine biosynthesis are located adjacent to one another in the chromosome. If excess histidine is present in the medium, the synthesis of all seven enzymes is coordinately repressed, whereas in the absence of histidine, all seven genes are coordinately expressed. Most mutations in this region of the chromosome result in the loss of activity of only one of the enzymes. However, mutations mapping to one end of the gene cluster result in the loss of all seven enzymes, even though none of the structural genes have been mutated. In what region of the his operon does this type of mutation occur? Explain your answer.

Explanation / Answer

Most mutations in this region of the chromosome result in the loss of activity of only one of the enzymes.Explain how such a mutation would only effect the production of one enzyme. What is the counterpart of this type of mutation in the lac operon system? Mutations resulting in the loss of activity of only one enzyme would be mutations to a single structural gene. These mutations would be like a lacZ- or lacY- mutation. b)Some mutations, mapping to one end of the cluster of histidine biosynthesis genes, result in the loss of all seven enzymes, even though none of the structural genes have been lost.Explain how such a mutation could effect all seven genes. What is the counterpart of this type of mutation in the lac operon system? Mutations that result in the loss of activity of all seven enzymes would have to be mutations to the regulatory regions of the operon. These mutations would be similar to lacP- mutations.

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