You are interested in studying the transcriptional regulation of the Gip1 promot

Question

You are interested in studying the transcriptional regulation of the Gip1 promoter. The Gip1 promoter contains a binding site for the Jk8 protein that overlaps with the binding site for the Pa5 protein. Jk8 and Pa5 cannot bind DNA at the same time, but both proteins are present at high levels in adult liver cells. The binding sites for Jk8 and Pa5 are shown in Figure Q8-33. Jk8 binds to site A while Pa5 binds to site B. You create mutations that remove the nonoverlapping sequences of either binding site A or B, and examine Gip1 mRNA production in adult liver cells that contain these mutations. The data you from these experiments are shown in Table QB-33. You know that Gip 1 is only expressed in adult liver cells and not in the liver of embryos. You also know that Jk8 and Pa5 behave similarly on other promoters in the embryo or in the adult, in terms of whether they act as repressors or gene activators. Given the data, use of which of the following mechanisms would make the most sense for regulating the Jk8 and Pa5 proteins: Select one: a. Jk8, but not Pa5, is transcribed in embryonic liver cells. b. Jk8 is ubiquitylated and targeted for destruction in adult cells. c. Pa5 binds to the promoter of the gene that encodes Jk8 in embryonic liver cells. Jk8 binds to the promote of gene that encodes Jk8 in embryonic liver cells.

Explanation / Answer

Answer: (c) Pa5 binds to the promoter of the gene that encodes Jk8 in embryonic liver cells.

From the given data, it can be inferred that Jk8 is an activator and Pa5 is a repressor of transcription.

Since GlP 1 is not expressed in embryonic liver cells, Pa5 (repressor) binds to the promoter and inhibits transcription.

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