Question

The sequence of an estrogen-responsive element is given below.

What would you be the most likely consequence of the introduction of this sequence of about 200 bases upstream (-200) of the gene transcirption initiation site encoding the enzyme mucosa?

5' - TGGTCAGGCTGGCT-3

Answer 1

Estrogen responsive element is a DNA sequence which provide the binding site for the members of steroid receptor superfamily. This includes the estrogen receptor (ER) which captures the corresponding ligand i.e. estradiol or related derivatives. The binding of these steroid hormones like estradiol to the ER leads to the formation of hormone-receptor complex which travels to the nucleus and binds to the receptive sequence of the DNA. The site- specific binding of the Hormone-receptor complex to the desired DNA sequence leads to further downstream transcriptional activation thereby regulating the expression status of several genes.

According to this question, if a stretch of DNA is engineered such that the estrogen responsive element is introduced 200bp upstream of the stretch coding mucosal enzymes, then the expression of the mucosal enzyme is likely to get dependent upon the arrival of the signalling molecule, i.e. estradiol. When estrogen or related steroid hormone arrives and complexes to its corresponding receptor, i.e. ER, this will bind to the estrogen responsive element in the nucleus. Since this stretch of DNA sequence is located 200bp upstream of the mucous encoding gene, it will likely to function as a transcriptional regulator of the mucousal enzyme encoding gene. Hence, the expression of the respective mRNA and the protein/ enzyme of the downstream genes will become estrogen - dependent. Besides, if the binding of ER-hormone complex to the estrogen responsive element alters the feasibility of the binding of the transcription factors mediating mucosal gene transcription, the rate of transcription is likely to get altered. If the binding of transcription factors occurs with enhanced affinity, then mucosal gene transcription will increase. Alternatively, if the binding affinity decreases then the reverse effect is likely to occur on transcription and further protein expression.