Molecular Genetics

Experiments with tobamoviruses revealed that RNA, as well as DNA, could carry hereditary information.

Facts

A variety of strains of tobacco mosaic virus (TMV) exist. Many strains cause distinctive symptoms on indicator plants (A).

TMV particles can be dissociated into RNA and protein components. The separated RNA and protein can be mixed together to reform infectious viral particles (B).

Mixed particles, with RNA of one strain and protein of another, can also be formed. Mixed particles are infectious. Note the symptoms they produce (C).

Interpretations

• The type of symptoms produced by mixed particles are not due to the coat protein.
• Rather, the TMV nucleic acid carries the genetic information that determines symptom type.
• This experiment further strengthened the idea that nucleic acids were the carriers of genetic information.
• The process of introducing genetic information into a cell by encapsidating the nucleic acid in a viral or phage coat is known as transfection and is widely used in molecular cloning.

Further information

• The combinatorial mixing of viral RNA and capsid proteins of different tobamoviruses and their assembly into virions further suggested that the nucleic acid was the genetic material.
• The identification of progeny virions was confirmed by sequencing of the coat proteins.