In the 1952 Hershey–Chase experiment, phosphorus-32 tracked DNA inside bacteria.
Alfred Hershey and Martha Chase used bacteriophages, viruses that infect bacteria. They prepared one group of phages with DNA labeled using radioactive phosphorus-32 and another group with protein labeled using radioactive sulfur-35. DNA contains phosphorus in its phosphate backbone, whereas proteins can contain sulfur in certain amino acids.
After the phages infected Escherichia coli, the researchers used a blender to detach viral coats from the bacterial cells and centrifuged the mixture. Most of the phosphorus-32 entered the bacteria, while most of the sulfur-35 remained with the external phage coats. New phages produced inside the bacteria also inherited the DNA label.
The experiment showed that DNA, rather than protein, is the genetic material of the phage. Sulfur-35 was the protein label in the paired comparison, but it did not track the hereditary material into the cells.