Galactose breakdown in yeast requires 5 enzymes. If galactose is not present, the genes encoding these enzymes are not active. When galactose is added transcription increases ~1000x. The genes are widely separated, some are even on different chromosomes. How is expression of this group of enzymes coordinated?

Options for the question are not given. They are as follows:

A. Include binding sites for the same general transcription factors in the promoter of each gene.

B. Include binding sites for different general transcription factors in the promoter of each gene.

C. Include binding sites for the same activators/specific transcription factors in the enhancer elements of each gene.

D. Include binding sites for different activators/specific transcription factors in the enhancer elements of each gene.

Answer:

C. Include binding sites for the same activators/specific transcription factors in the enhancer elements of each gene.

Explanation:

Promoter region is responsible for the initiation of transcription. Transcription factor binds to it and the process begins. Enhancer region increases the rate of transcription. Unlike promoter, it is not required for the an enhancer to be located near the gene.

Here genes responsible for the production of galactose metabolizing enzymes are located far from each other. But they all should work together at the same time in presence of galactose. To make sure this happens, activator molecules are present. In presence of galactose a set of activator molecules begin functioning together. They bind to all the enhancers at the same time so that the genes can become active. Gal3p and Gal4p are such activators which recognize the Upstream Activator Sequence (UAS).