Tobacco Mosaic Virus (TMV)

Scientists: Conducted by H. Fraenkel-Conrat and B. Singer in 1957.

Subject: Tobacco Mosaic Virus (TMV), which is composed of 6% RNA surrounded by a hollow protein coat cylinder. It contains zero DNA.

Procedure:

• The researchers separated the RNA from the protein coat of TMV viruses.
• They formed "reconstituted" (hybrid) viruses by combining the protein from one mutant strain with the RNA from a different mutant strain.
• These hybrid viruses were then used to infect tobacco leaves.

Results: In every case, the examined progeny matched the parental RNA type, not the parental protein type.

Experiment of Fraenkel-Conrat on TMV showing that RNA is the genetic material in RNA-containing viruses

Diagram Observations:

• Intact TMV particle → causes infection.
• Isolated protein subunits → no infection.
• Isolated RNA → causes infection.
• Reconstructed virus → causes infection.

Conclusion: The experiment successfully demonstrated that RNA is the genetic material in RNA-containing viruses like TMV.

• Fraenkel-Conrat and Singer (1957) proved RNA is the genetic material in Tobacco Mosaic Virus (TMV).
• TMV lacks DNA; it consists of 6% RNA surrounded by a hollow protein coat.
• They created hybrid viruses by mixing the RNA of one mutant strain with the protein coat of another.
• When infecting tobacco leaves, the viral progeny always matched the parental RNA type, never the protein type.
• Infection occurs with intact TMV, isolated RNA, and hybrid viruses, but isolated protein subunits cannot cause infection.