Hershey-Chase experiment

The Hershey-Chase experiment distinguished the behavior of DNA and coat proteins during infection by Bacteriophage T2. In their 1952 study, A. D. Hershey and Martha Chase followed phosphorus-32 associated with phage DNA and sulfur-35 associated with phage proteins. The labels made chemically different parts of the same kind of virus experimentally distinguishable.^[ref]

After the bacteriophages attached to bacteria, a Waring blender sheared off much of the material remaining outside the biological cells. Centrifugation separated a cell-containing sediment from the surrounding liquid. Most sulfur label stayed outside, whereas most phage phosphorus remained with the biological cells; the treated bacteria could still yield progeny bacteriophages. Comparing label in progeny supplied a further test beyond attachment alone.^[ref]

An original accounting example illustrates the logic: if a tracer gives 80 corrected units with cells and 20 outside, its cell-associated fraction is $80/(80+20)=0.8$. Comparing that fraction for the two labels tests their different destinations. It does not measure an 80-percent share of heredity. Label specificity, incomplete separation and recovery matter.

The result supports entry of DNA while much coat protein remains external. It neither establishes that every protein molecule stays outside nor excludes all other entering material. The paper explicitly limits further chemical inferences.^[ref]