Hershey–Chase experiment

With become known as the Hershey - Chase experiment experiment could be demonstrated that genetic information is encoded in DNA and not proteins. The experiment was conducted in 1952 by Alfred Hershey and Martha Chase. It provided an independent confirmation of the result had received in 1944 Oswald Avery, Colin MacLeod and Maclyn McCarty in their tests for genetic transformation of bacteria.

In Hershey -chase experiment viruses were used, which are specialized in the infection of bacterial cells. Such viruses are called bacteriophages ( ' bacteria -eaters ') or phages. They consist essentially of a protein coat and DNA purified (rarely RNA). When they hit a bacterium, they put their tail attachments on the bacterial surface and inject their entire DNA into the bacterium. The protein shell, however, remains outside the bacterium. The injected DNA stimulates the bacteria to build new phages ( self-assembly ), which will eventually be released by destroying the bacteria.

Hershey and Chase now cultivated phage called T2 phage, even with the addition of radiolabeled sulfur ( 35S ), and in a second petri dish with the addition of radiolabeled phosphorus ( 32P ). The radioactive labeled sulfur was this built into the proteins. The radiolabeled phosphorus in the other petri dish was, however, incorporated in the DNA of the grown phages.

Then the phage were each bacteria (Escherichia coli), which had no radioactively labeled substances, is added. Shortly after the phage had been placed on the bacteria and injected their DNA, Hershey and Chase gave the samples in a blender. The shearing force of the mixer was sufficient to release the empty phage envelope protein from the bacterial surface, but neither the sleeves nor the bacteria were destroyed. In a subsequently performed centrifugation the heavy bacteria deposed in the sediment, while the lighter phage coats remained in the supernatant.

In the samples in which the proteins were labeled with the aid of the 35S, were able to measure the radioactivity in the supernatant Hershey and Chase. The proteins were therefore not entered the bacteria, since these were located exclusively in the sediment, which had no radioactivity. In the samples in which the DNA was labeled with 32P using the other hand, the radioactivity was found exclusively in the sediment. This was the proof that DNA penetrated into the bacteria. Only the DNA could animate the bacteria for the production of phage by means of the genetic information carried by it.

• Genetics
• Biological experiment