6 Mechanisms that Regulate Transcription of a Gene by RNA Polymerase

Important Mechanisms Which Can Regulate the Transcription of a Gene by RNA polymerase are listed below:

1. Specificity factors alter the specificity of RNA polymerase for a given promoter or set of promoters, making it more or less likely to bind to them (i.e. sigma factors used in prokaryotic transcription).

2. Repressors bind to non-coding sequences on the DNA strand that are close to or overlapping the promoter region, impeding RNA polymerase’s progress along the strand, thus impeding the expression of the gene.

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3. General transcription factors these transcription factors po­sition RNA polymerase at the start of a protein-coding se­quence and then release the polymerase to transcribe the mRNA.

4. Activators enhance the interaction between RNA polymerase and a particular promoter, encouraging the expression of the gene.

5. Activators do this by increasing the attraction of RNA polymerase for the promoter, through interactions with sub- units of the RNA polymerase or indirectly by changing the structure of the DNA.

6. Enhancers are sites on the DNA helix that are bound to by activators in order to loop the DNA bringing a specific pro­moter to the initiation complex.

There are only two types of gene regulation: positive regula­tion and negative regulation. When the expression of genetic in­formation is quantitatively increased by the presence of a specific regulatory element, regulation is said to be positive and when the expression of genetic information is diminished by the presence of a specific regulatory element, regulation is said to be negative.

The element or molecule mediating negative regulation is said to be a negative regulator or repressor; that mediating positive regu­lation is a positive regulator or activator. However, a double nega­tive has the effect of acting as a positive.

Thus, effectors that inhibit the function of a negative regulator will appear to bring about a positive regulation. Many regulated systems that appear to be induced are in fact depressed at the molecular level.