In the Hershey–Chase experiment of 1952, DNA entered bacteria when bacteriophages infected them.
Alfred Hershey and Martha Chase used bacteriophages, viruses that infect bacteria. A phage consists mainly of DNA inside a protein coat. They labeled phage DNA with radioactive phosphorus-32 and labeled phage protein with radioactive sulfur-35, because DNA contains phosphorus while proteins can contain sulfur.
After the phages attached to Escherichia coli, a blender separated the empty virus coats from the bacterial cells. Most of the phosphorus label was found with the bacteria, while most of the sulfur label remained with the detached coats. The result indicated that DNA entered the cells and directed production of new phages.
The experiment did not prove that protein has no biological function; phage proteins form the protective outer structure and help with infection. Its specific significance was identifying the material transmitted into the host during this type of viral infection. It strengthened the case that DNA is genetic material.