1. Experiments conducted by Fraenkel-Conrat and Singer on tobacco mosaic virus (TMV) provided evidence that RNA can act as genetic material. 2. They were able to separate the TMV into RNA and protein components, and found that RNA alone was able to cause infection when introduced into tobacco plants, demonstrating that RNA carries the genetic information. 3. They also generated chimeric viruses by combining the RNA of one TMV strain with the proteins of another strain. These chimeras displayed characteristics dependent on the source of the RNA, not the proteins, proving that the specificity of viral proteins is determined by the RNA.

1. K. Narayanapura, Kothanur (PO), Bengaluru 560077
Tel+91 80 – 68737777 / 28465770 /28465353 Fax. 080- 68737799
e-mail:info@kristujayanti.com, www.kristujayanti.edu.in
Experimental Evidence to
prove RNA as genetic material
Dr. Manikandan Kathirvel
Assistant Professor,
Department of Life Sciences,
Kristu Jayanti College (Autonomous),
Bengaluru

2. While DNA is the genetic material for the vast majority of organisms, there are some viruses that use RNA as their
genetic material.
These viruses can be either single or double stranded and include SARS, influenza, hepatitis C and polio, as well as the
retroviruses like HIV-AIDS.

3. RNAAS GENETIC MATERIAL
Experiments with tobacco mosaic virus (TMV):
With the help of transformation experiment and bacteriophage infection, it was shown that DNA is the genetic material.
RNA is the genetic material in viruses was demonstrated in 1956 with the experiments conducted on tobacco plant by A.Gierer
and G.Schramm.
1. All viruses are not limited to bacterial hosts.
2. Viruses infect and parasite plant cells, and even some animal cells contain RNA only. In these viruses, RNA act as genetic
material.
3. One plant virus, Tobacco mosaic virus(TMV), that contains RNA, not DNA was an important tool for genetic Experiments.
4. TMV infects tobacco, causing the infected regions on leaves to become discolored and bristled. Different strains of TMV
produce clearly different inherited lesions on the infected leaves.
5. The common TMV virus produces a green mosaic disease, but a variant Holmes rib grass(TMV-HR), produces ring
spot lesions. Moreover, the amino acid compositions of the proteins of these two strains differ.

4. H.Fraenkel-Conrat and B.Singer Experiment:
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 surrounded by a hollow cylinder of
protein subunits.
H.Fraenkel-Conrat and B.Singer first developed the techniques for separating
TMV particles into RNA and protein.
• They used RNA and proteins separately in tests for infectivity, it could be shown
that RNA alone was able to cause infection. Such a property was not found in
the protein fraction.
• They found that virus could be broken into component parts and they could
again be reassembled or reconstituted to form functional virus.
• It was possible to synthesize chimeric virus particles using RNA from one strain
and protein from another strain.
When these reassembled viruses were used to infect tobacco leaves, the progeny
viruses produced were always found to be phenotypically and genotypically
identical to the parent strain from which the RNA had been obtained.
Such chimeras had serological properties of those strains from which protein was
derived, but in other properties, it resembled the other strain from which RNA was
used.

5. In one experiment, two viruses used
were tobacco mosaic virus (TMV) and
Holmes rib-grass virus (HRV) (isolated from Plantago
lanceolata and therefore, is also known as Plantago strain).
Proteins of these two viruses differ in having different
frequencies and sequences of amino acids.
Also these viruses give different symptoms.
On leaves of a particular variety of tobacco,
• while TMV produces mottling of leaves,
• HRV produces distinct ring patterns.
Reciprocal chimeras using RNA of one strain and protein of the
other strain could be obtained.
It was found that when these chimeras (hybrid) were used for
infection, the progeny had proteins which corresponded to the
virus from which RNA of the infecting virus particles was
derived.
This proved that specificity of virus proteins was determined by
RNA alone and that proteins carried no information.

6. The reassembled viruses with the TMV-common
RNA and TMV-HRV protein produced a green
mosaic disease characteristic of TMV-common.
Recovered virus had protein characteristic of TMV
common.
This proved that specificity of virus proteins was
determined by RNA alone and that proteins carried
no genetic information. Hence RNA carries genetic
information not proteins.
The genetic RNA is usually found to be single
stranded but in some it is double stranded as in
reovirus, wound tumor virus.

7. Thank you