Hershey-Chase experiment

 

Hershey-Chase experiment         

In 1952, Alfred Hershey and Martha Chase performed the Hershey-Chase Experiment, which identified DNA as the phage genetic material. A phage is a bacteria-infecting virus. It comprises a protein coat containing dsDNA. As phases consist of protein-based nucleic acid only, they are ideal to determine if the protein or nucleic acid is the genetic material.

Hershey and Chase conceived an experiment using radioactive Sulfur and phosphorous isotopes to monitor viral proteins and nucleic acids separately during the process of infection. The T2 bacteriophage and the Escherichia coli bacterium were used. The phages were indicated by infecting in the cultivation medium bacteria with radioactive isotopes ³⁵S. Hershey & Chase identified the material injecting into the cell by phases attached to the bacterial wall.

When ³²P-labeled phages were mixed with unlabeled E. coli cells, Hershey and Chase found that the ³²P label entered the bacterial cells and that the next generation of phages that burst from the infected cells carried a significant amount of the ³²P label. When ³⁵S-labeled phages-were mixed with unlabeled E. coli, the researchers found that the ³⁵S label stayed outside the bacteria for the most part.

Hershey and Chase thus showed that the outer protein coat of the phage does not enter the infected bacterium while the internal the material of the phage, consisting of DNA, enters the bacterial cell, and as DNA is the producer of a new phage, during the infection process, the genetic the material should be DNA, not the protein. Hershey shared 1969 Nobel Prize in Physiology or Medicine for his discoveries concerning the genetic structure of viruses.