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RNA as a Genetic Material.

Posted by Mumtaz khan Wednesday, 18 January 2012

       As more and more viruses were identified and studied it became clear;that many of them contain RNA and proteins,but no DNA.In all cases studied till date it is clear that these RNA viruses store their genetic information in nucleic acids rather than in proteins.Just like all other organisms Although in these viruses,the nucleic acid is RNA.
          The demonstration that RNA is genetic material in RNA containing viruses,came in 1956,when Gierer and Schram,showed that,the tobacco plants could be inoculated with purified RNA from the tobacco Mosaic Virus
(TMV) and TMV like lesions could later be identified in tobacco leaves.One of the first experiments that established RNA as genetic material in RNA viruses was the so called reconstitution experiments of Fraenkel-Conrat and singer published in 1957.Conrat and Singer's simple but definitive experiment was done with TMV. A small virus composed of single molecule of RNA,encapsulated in a protein coat.Different strains of TMV in chemical composition of their protein coats.
         By using the appropriate chemical treatments one can be separate,the protein coats of TMV from RNA.Moreover this process is reversible and by mixing the proteins and RNA under appropriate conditions reconstitution will occur giving complete infective TMV particles.Conrat and Singer took 2 different strains of TMV, separated the RNA's from their protein coat and then reconstituted mixed viruses, by mixing the proteins of one strain withthe RNA of the 2nd strain and vice versa.
When thse mixed viruses were used to infect the tobacco leaves,the phenotypically and genotypically identical to the parent strain from with the RNA had been obtained.Thus,the genetic information of TMV is stored in RNA and not in Protein.


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