3. Assume that in a bacterial species you discover a cluster of three genes ( A

Question

3. Assume that in a bacterial species you discover a cluster of three genes (A, B, and C) that account for the enzymatic production of a cellulose-like carbohydrate (clc) that is needed as a component of its cell wall. When there is sufficient clc is in the cell, the three enzymes are not synthesized. However, when more clc is needed, the three enzymes are abundantly produced. This cluster of genes appears to be under coordinate control because deletion of a distant gene (R) results in constitutive expression of all three genes even when excess clc is present. When mutations (P -) occur in a region upstream of gene A, no synthesis of the three enzymes occurs even when clc levels are extremely low. Mutations (O -) that occur right next to the P - mutations result in constitutive expression of all three genes even when clc is present at high levels.

(a) Do the three genes (A, B, and C) behave as if they were part of an operon?

(b) What type of control (positive or negative) seems likely to control the production of the three enzymes?

(c) What is the most likely function of the protein produced from gene R?

(d) Do you expect that clc is an inducer, inhibitor, or corepressor?

(e) You discover that clc binds to the protein made from gene R. What is the most likely effect of this binding? (Hint: will it cause the R protein to bind DNA or fall off of the DNA?)

(f) Where do you think protein R binds? (Hint: P region or O region ?)

Explanation / Answer

A it seems a appears all three gene are part of operon as cluster of gene are controlled by a single distant gene R.

B. This is example of negative control because the end product enzyme repression cause induction of gene and more end product suppression the gene induction

C. Mostly it looks the gene R product , protein R acts like a repressor because normal R gene repress the three gene activity.

D. Clc would be a co repressor, because end if clc is more genes are actively producing the product due R protein .

E. R bind to clc and would not bind to DNA and fall off so can not induct gene. And repress it.

F. It seemse it should bind to O region so not binding cause more. Induction.

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