Structural Biochemistry/Enzyme Regulation/Transcription activation

Overview

Transcription activation is the regulation by which a change in the rate of DNA transcription may alter the expressed gene in question. Regulatory proteins are utilized to activate an expression of a certain gene or to repress it (regulate). The activators catalyze interaction of RNA polymerase in the synthesis or expression of the gene in hand. This is accomplished by increasing the binding affinity of the RNA polymerase to the promoter site, the region of DNA that is vital in the transcription process. Transcription factors are activated, and transcription occurs at the promoter site. Histone interactions occur during acylation as DNA is transcribed into RNA.

Mechanism

First, the binding of a ligand to a certain receptor occurs, initiating a reaction signal. This activates a transcription factor, which is a protein that binds specific DNA sequences and controls the rate of the transcription process. The transcription factor additionally binds to other reagents necessary in transcription. These proteins (transcription factors) are then able to be regulated by reversible regulation processes such as phosphorylation or proteolysis.

The transcription of DNA to RNA and its subsequent translation to proteins can be regulated by acylation and methylation. DNA is negatively charged and is wrapped around positively charged histone proteins. In order for transcription to occur the DNA must be unbound to the histones. This is accomplished by acylating the positively charged residues found in the histones such as lysine. This neutralizes the positive charge allowing for a looser binding with DNA. This allows RNA polymerase to enter and transcribe the desired gene. In order to reverse this effect and tighten the binding, methylation occurs. Methylation of the residues restores the positive charges to restore the electrostatic interactions between the histones and DNA and tighten the binding. It is in this method that gene expression is regulated.

References

1. Berg, Jeremy M. (2007). Biochemistry, 6th Ed., Sara Tenney. ISBN0-7167-8724-5. pp. 902-903. 2. Campbell, Neil A. Biology. 7th ed. San Francisco, 2005.