Question

A newly identified bacterial strain needs nedine as a growth factor. To synthesize nedine these bacteria use three enzymes that are encoded by the genes nedA, nedB and nedC in the ned operon. The expression of these three genes is controlled by a regulatory protein NedR. Nedine binds to NedR, and it changes the ability of NedlR to bind to the regulatory region of the ned operon. The ned genes are expressed only in the absence of nedine. The regulator NedR, only when bound to nedine, can bind at the regulatory region of the ned operon

Answer the following questions and provide an explanation for each answer      

1. Is the ned operon inducible or repressible?
2. Is the NedR a positive or negative regulator?

Answer 1

1) Ned operon is repressible. This is because the ned genes are expressed only in the absence of nedine. It can be explained using feedback repression. Here 3 enzymes are needed for the synthesis of end product nedine. These enzymes are synthesized by the activity of 3 different genes in the coordinated manner. The addition of nedine, however, stops the production of these enzymes. Thus, this system is known as repressible system.

2) NedR is a positive regulator because regulator NedR, only when bound to nedine, can bind at the regulatory region of the ned operon