1. Steroid hormones are known to increase the expression of specific genes in se
ID: 32734 • Letter: 1
Question
1.Steroid hormones are known to increase the expression of specific genes in selected target cell types. Testosterone increases the production of a protein called alpha-2-microglobulin (?2m) in the liver and hydrocortisone (a glucocorticoid) increases the production of tyrosine aminotransferase (TAT) in the liver. (Each hormone does many other things). All steroid hormone receptors consists of 3 related, but distinct, protein domains: a hormone binding domain, a DNA binding domain, and a regulatory domain.
A.How is it that testosterone and hydrocortisone can selectively influence the expression of two different genes in the same tissue?
B.By what you know of domains, suppose you carry out a domain swap experiment to exchange the DNA binding domains of testosterone receptor and glucocorticoid receptor with each other. What effects would you now expect the two hormones to have in cells containing the altered receptors?
Explanation / Answer
A. Testosterone is an androgen receptor; while hydrocortisoe is a glucocorticoid receptor. These receptors are also known as transcription factors. When steroid hormone, (in this case testosterone and hydrocortisone) binds to these receptors, these receptors are activated. They move into the nucleus by the aid of nuclear localisation signals, and in the nucleus transcription of the specific gene of interest takes place. So , we can say that it is the type of receptor which is responsible for selective expression of two different genes.
B. DNA binding domains controls which gene will be activated. So, if the DNA binding domains of testosterone receptor and glucocorticoid receptor are exchanged with each other; then the above effect of testosterone and hydrocortisone will be reversed; means Testosterone increases the production of TAT In the liver and hydrocortisone (a glucocorticoid) increases the production of alpha-2-microglobulin
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