Hershey–Chase experiment: demonstration that DNA is the genetic material

Experimental design and key steps

The experiments relied on the chemical differences between proteins and DNA. The team labeled the protein coat of bacteriophage T2 with radioactive sulfur-35 and labeled the viral DNA with radioactive phosphorus-32. They then allowed labeled phages to infect Escherichia coli cells and used a blender to shear off viral coats after the initial infection step.

1. Label phage proteins with sulfur-35 and phage DNA with phosphorus-32.
2. Allow phages to attach to and inject material into bacteria.
3. Separate viral coats from infected cells by agitation and centrifugation.
4. Measure radioactivity in the bacterial pellet versus the supernatant.

Radioactivity from phosphorus (DNA) was found inside the bacterial cells, in the pellet, while radioactivity from sulfur (protein) remained mostly in the liquid supernatant. This indicated that DNA entered the cells and was responsible for directing production of new phages.

Context and historical background

The Hershey–Chase results complemented earlier work such as the Avery–MacLeod–McCarty transformation experiments and followed rapidly after the first structural models of DNA. The conclusion that DNA was the hereditary material helped shape the field of molecular genetics and supported subsequent efforts to decode how genetic information is stored and expressed. For biographical context, see Alfred Hershey and Martha Chase in related biographies: Hershey and Chase.

Importance and legacy

• Definitive evidence: The experiment provided straightforward, reproducible evidence that genes are carried by DNA rather than by protein.
• Impact on virology: It clarified the nature of viral replication and informed later research on virus genetics and replication mechanisms (viruses).
• Recognition: Alfred Hershey later received international recognition for his contributions to understanding viral genetics; the work is often discussed in general histories of genetics and molecular biology (overview).

Notable distinctions and caveats

While the Hershey–Chase experiments are elegant and persuasive, they were one part of a larger body of evidence establishing DNA as genetic material. The experiments used a virus-bacterium system, so extrapolation to all life required integration with other studies. Nonetheless, their clarity and simplicity made them a cornerstone proof in textbooks and courses on genetics and molecular biology.

For concise background on DNA and genetic concepts see resources on DNA and genetic material, and for further reading about experimental approaches of that era consult additional historical summaries and primary literature summaries at recommended links: biographical note and technical perspectives.