Everything about RNA — Part 3

RNA, Everything about it.

I read and refer Harper's Biochemistry from Lange Publications.
Visit their Website at http://www.lrpub.com

I relied extensively on Lehninger for this article. Solid book, timeless. From Worth Publishers Inc.

Introduction
Synthesis of an mRNA molecule Part 1
Synthesis of an mRNA molecule Part 2
Termination of mRNA synthesis

This article is the first in a four-part series on RNA. Still to come are
1. Post-transcriptional processing of RNA
2. tRNA and rRNA and hnRNA
3. Retroviruses

Termination of RNA synthesis:-
There are two known mechanisms of termination of transcription in bacteria. They are the rho dependant and the rho independant termination methods.

The rho-independant class has two features. The first one is an end sequence of bases which are self-complemantary if the mRNA chain is bent upon itself so as to form a hairpin like structure at the end. This is followed by a polyadenylate run on the parent DNA which codes for a poly uridylate chain on the RNA.

Dissosciation follows quickly, after transcription of the rho-independant terminating sequence as the polyuridylate chain and the hairpin pull away the mRNA molecule from the transcription bubble.

rho-dependant termination sequences do not contain the polyadenylate run on the DNA, but an ATP dependant rho protien dissosciates the mRNA strand from the transcription bubble as soon as a short palindromic(hairpin forming) sequence is transcribed.

Eukaryotic cells contain three types of RNA polymerase, I, II, III. RNA polymerase I is involved solely in the formation of the long preribosomal RNA transcript. Pol II synthesizes all the cellular mRNAs. Pol III creates tRNAs.

Name of the toxin/substance	Postulated mechanism of action
Actinomycin D	Molecule inserts itself between successive G=C pairs and disrupts the transcription bubble.
Acridine	A similar method
Rifampicin	Binds to the beta subunit of bacterial RNA polymerase and prevents initiation of transcription