Question

estrogen + estrogen estrogen + estrogen estrogen + estrogen (fig68) anti-ER anti-H3K27AC Input DNA PCR: estrogen response element (ERE) in black region Set 1 Set 2 Set 3 Because MYC showed higher expression in the ovarian tumor exposed to estrogen, you suspect MYC may be regulated by the estrogen hormone receptor, a nuclear receptor. To see if the estrogen receptor binds to the enhancer region in the tumor cells, you perform ChIP-PCR. The figure above shows three different sets of ChIP-PCR results, using antibodies for both estrogen receptor and for H3K27AC. A) If you know that the sequence of the estrogen response element (ERE) is an inverted repeat, which ChIP-PCR set would match your expectations? Explain. (3 pts) B) In the ChIP-PCR experiment above you are testing for the presence of the H3K27Ac histone mark. When this mark is present on nucleosomes, what is one histone mark would expect not to be on those nucleosomes? Why? (2 pts)

Answer 1

H3K27ac is an epigenetic modification to the DNA packaging protein Histone H3. It is a mark that indicates the acetylation at the 27th lysine residue of the histone H3 protein.

H3K27ac is associated with the higher activation of transcription and therefore defined as an active enhancer mark. H3K27ac is found at both proximal and distal regions of transcription start site (TSS).

A) Answer:- Set-3 ChIP PCR set would fulfill the expectation.

Explanation:- On the presence of estrogen, there are both expression of estrogen receptor and the acetylation at the 27th lysine residue of the histone H3 protein ( H3K27Ac) increases and which favours the binding at ERE also the transcription process.

B) As acetylation favours the process, deacetylation of H3 doesn't favours, so the absence of deacetylated H3 in the nucleosome will be wanted.