I have no idea how to answer this problem, I need help thanks. Explain if possib

Question

I have no idea how to answer this problem, I need help thanks. Explain if possible.

13. the gene that encodes the enzymes for arginine biosynthesis are regulated by a transcriptional regulator named ArgR. The activity of ArgR is modulated by arginine. Upon binding to arginine, ArgR alters its conformation, dramatically changing its affinity for the DNA sequences in the promoters of the genes for the arginine biosynthesis enzymes. ArgR is a repressor protein.

A. Do you expect that ArgR will bind moe tightly or less tightly to the DNA sequences when arginine is abundant?

B. How would expression of the arginine biosynthesis enzymes change of you make mutant ArgR that could not bind DNA?

C. How would expression of the arginine biosynthesis enzymes change of you make mutant ArgR that always binds DNA?

Explanation / Answer

Ans 13. A. ArgR is an arginine dependent aporepressor gene that depends on the concentration of co-repressor L-arginine. ArgR is a hexamer of identical subunits consisting of a N-terminal DNA binding domain which connects through a flexible linker to C-terminal domain responsible for oligomerization and arginine binding. when L-arginine binds with the c-terminal, it results in allosteric activation of the regulator. this active hexamer recognizes one or more “ARG box” DNA sequences made of 18-bp imperfect palindromes  and can act as a transcriptional inhibitor and/or activator, depending on the prokaryotic species. For example, in B. subtilis in the presence of arginine, the arginine repressor inhibits arginine biosynthesis and activates the arginine catabolic arginase pathway. it clearly indicates DNA binding is initiated by arginine concentration. If DNA binding will occur regulatory pathway will follow and arginine biosynthesis will not occur.

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