Question

1. Gene B is usually expressed only in skin cells. To learn about the mechanism by which expression of the gene B is regulated, you make clones that contain a GFP reporter and various parts of the upstream and downstream intergenic regions of genomic DNA that normally surround gene B (black lines) as shown in the figure below. The resulting clones were introduced into frog skin cells growing in the lab and levels of GFP expression was monitored by measuring green fluorescence. The table at left shows relative GFP expression, with more +s equal to more expression. (one + = basal expression). Normalgene 8 structure gene 8 Expression A B C D of GFP in skin cells GEP Normal gene B expression level +++ Reporter constructs +++ +++ a. Which area(s) are likely to contain a cis-acting regulatory element? (1 pt) b. Which area contains the gene B promoter? (1pt) c. Which area contains an enhancer? (1 pt) d. Which area is likely to bind to proteins that activate gene B (an activator)? (1 pt)

Answer 1

1) B & D

Cis-acting regulatory element are non-coding DNA segments that regulate the transcription of neighboring genes. So, a genetic element that causes any change in expression level may be a cis-acting regulatory element. We see, that upon deletion of B and D, there is a decrease in GFP expression, hence these are CREs.

2) Promoter - D

With the loss of a promoter region, there will be no expression of the gene/GFP because of the failure of RNA polymerase binding to the gene element.

3) Enhancer - B

Element B is the enhancer because its loss causes a decline in GFP level, but the gene is not completely silenced, hence it can only be an enhancer.

4)Activator - B or D

The loss of an activator element will cause a decline in the resultant protein product. We know that D contains the promoter element, but we are not sure how much of D contains the promoter element, hence B or D may be an activator of the gene B.