RNA AS A GENETIC MATERIAL

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The first evidence that RNA also has the capacity to

carry genetic information came from experiments conducted with tobacco mosaic virus (TMV).

This virus does not contain any DNA, and is composed of RNA (6%) surrounded by a hollow

cylinder of protein subunits. The experiments conducted by H. Fraenkel-Conrat and B. Singer

showing that RNA is the genetic material.

Techniques were first developed for separating TMV particles into RNA and proteins. Later by

using RNA and proteins separately in tests for infectivity, it could be shown that RNA alone was

able to cause infection. Such property was not found in the protein fraction.

When the cell debris (Protein coat) of the virus was introduced in to tobacco leaf, the leaf

remained healthy. When the cell filtrate (nucleic acid) was injected into tobacco leaf, it was

infected with the virus and died. This shows that the RNA is causing the infection and not the

protein. The progeny viruses produced were always found to be phenotypically and

genotypically identical to the parent strain from which the RNA has been obtained.

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