Question

Consider the lac operon in E. coli.

a. List the cis-acting elements and the trans-acting factors involved in the regulation of its expression.

b. Indicate which Transacting factors interact with which cis-elements.

c. Describe what the factors do when they are bound to their respective cis–elements.

d. Indicate the inducer in this system and how it works.

Answer 1

a) lacO is the cis-acting element which is the operator site for the lac operon. LacI is the trans-acting protein that binds to the lacO region to regulate the operon expression.

b) LacI protein interacts with the cis-element.

c) When the LacI protein is bound to the lacO region, the operon expression will be repressed.

d) Allolactoose is the inducer of the system which is a metabolic product of lactose by the help of enzyme beta-galactosidase. The allolactose binds to the LacI and releases the LacI protein from the lacO site, thereby inducing the lac operon expression.