Alfred Hershey and Martha Chase (1952) worked with viruses that infect bacteria called bacteriophages.

They used radioactive sulphur (³⁵S) to identify protein and radioactive phosphorus (³²P) to identify the components of nucleic acid.

The tadpole shaped bacteriophage attaches to the bacteria. Its genetic material enters the bacterial cell by dissolving the cell wall of bacteria. The bacterial cell treats the viral genetic material as if it was its own and subsequently manufactures more virus particles. Hershey and Chase worked to discover whether it was protein or DNA from the viruses that entered the bacteria.

The Hershey-Chase Experiment

They grew some viruses on medium that contained radioactive phosphorus and others on medium that contained radioactive sulphur. Viruses grown in the presence of radioactive phosphorus contained radioactive DNA but not radioactive protein because DNA contains phosphorus but protein does not. Similarly, viruses grown on radioactive sulphur contained radioactive protein but not radioactive DNA because DNA does not contain sulphur.

Radioactive phages were allowed to attach to E. coli bacteria. Then as the infection proceeded, the viral coats were removed from the bacteria by agitating them in a blender. The virus particles were separated from the bacteria by spinning them in a centrifuge.

Bacteria that were infected with viruses that had radioactive DNA were radioactive, indicating that DNA was the material that passed from the virus to the bacteria. Bacteria that were infected with viruses that had radioactive proteins were not radioactive. This indicates that proteins did not enter the bacteria from the viruses. DNA is, therefore, the genetic material that is passed from virus to bacteria.