. The diagram below shows the DNA sequence of a gene which is expressed only in

Question

. The diagram below shows the DNA sequence of a gene which is expressed only in the skin of the Jackalope, a diploid eukaryote. Shown is DNA sequence from close to the transcriptional start site, as well as some upstream sequence. The first nucleotide transcribed is an A, and the corresponding A on the coding strand is underlined. Two other sequences in this region are underlined.

Below the sequence is shown the structure of several pieces of DNA that I tested for their ability to initiate transcription. Construct a is the wild-type sequence and b through f either contain small deletions (b-d) or point mutations (e, f). At the right are indicated the relative levels of transcription for each construct, in Arbitrary Units.

i. For each mutant construct (b-f), indicate: what sequence element might be affected and why the expression level is changed to the extent shown.

Explanation / Answer

Construct b: the upstream enhancer region is deleted, which resulted in decreased gene expression. This region may be necessary for binding of proteins of pre-initiation complex.

Construct c: The TATA box or the core promotor region is deleted, but the upstream enhancer region is intact. Only minimal expression of the gene occurred

Construct d: Both upstream enhancer region and core promotor region are deleted. There is a total absence of gene transcription

Construct e: A point mutation in the promotor region made it a strong promotor or increased the binding strength of the promotor, which resulted in enhanced trasncription activity

Construct f: A point mutation resulted in loss of activity of the promotor region, or the promotor strength is greatly reduced

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