Hershey and chase worked with viruses that infect bacteria i.e. bacteriophages, which are composed of DNA and protein. When viruses infect bacteria, their genetic material is injected in the bacterial cell. Hershey and Chase worked to discover whether it was DNA or protein.
They used radioactive phosphorous( 32P) in the medium for some viruses and radioactive sulphur ( 35S) For some others. DNA contains phosphorous and not sulfur while proteins contain sulphur and not phosphorous. Therefore some viruses were with radioactive DNA and some with radioactive protein coat.
Boat the types of radioactive viruses were allowed to infect E. coli bacteria. As the infection proceeded, the viral coats were removed with help of centrifuge.
Bacteria which were infected by viruses with radioactive DNA were radioactive while the bacteria which were infected by viruses with radioactive protein were not radioactive. This indicates that DNA enters the bacterial cells and not proteins. Therefore DNA is the genetic material.