Hershey, A.D. & Chase, M. (1952) Independent functions of viral protein and
 nucleic acid in growth of bacteriophage. Journal of General Physiology 36:39-56.

 Alfred Hershey (1908 - 1997) and Martha Chase  (1930 - 2003)       

The race for DNA
 In 1953 Watson and Crick published their paper on the discovery of the structure of DNA

This marked the end of a legendary race, which, among its large case of characters, included Martha Chase and Alfred Hershey.

The Hershey and Chase paper was published shortly after Linus Pauling published seven papers detailing the molecular structure of protein and advocating his belief that protein was the genetic material.

At this time the only evidence for DNA as the genetic material was Avery's 1944 paper on Pneumococcus bacteria, which was largely ignored.

The results of Hershey and Chase's paper convinced even Pauling that he had been on the wrong track with protein and that DNA was most likely the genetic material.

These results caused a renewed interested and determination amongst many scientists of the time (esp. Watson) to find the structure of DNA.

Purpose: 
A single bacteriophage attaches to a bacteria cell, the bacteria lyses releasing numerous progeny. The question was:
How does the bacteriophage make multiple copies of itself?
There must be some sort of genetic information transferred from phage to cell!
Now all someone had to figure out was.....
WHAT IS IT???
The experiment was designed to determine, by means of radioisoptoping techniques, the function of viral protein and nucleic acid in the multiplication of bacteriophage.

Material and Methods:
T2 phage
 Glycerol-lactate medium
1 Waring blender
P³² and S³⁵

Results:

The commonly known 'Hershey - Chase" or "Blender" experiment is actually a series of experiments, each of which contributed significantly to the results as a whole.

Experiment 1:
 Induced osmotic shock » inactivates phage »  DNA released »  "ghosts" observed in micrographs. 
Showed DNA and protein are capable of being separated.
Also showed that protein component contained 90% of labeled sulfur, DNA component 80% of labeled phosphorus.

Experiment 2:
 The above expt. suggests that protein coat is removed or altered prior to replication.
 This was measured by the sensitivity of the DNA to DNase, as the protein coat provides protection against DNase.
Found that DNA was indeed susceptible after adsorption to bacteria that were heat killed either before or after infection.

Experiment 4:
 The DNA is ejected from the protective coat ( INTO the cell) after adsorption!

Experiment 5:
 If bacteria attach by propsed tail method it would bepossible to separate protein coats from the cells by agitation
A more definite determination of what gets inside the cell and what stays outside.
To accomplish this Hershey and Chase simply spun a suspension of infected cells in a Waring blender.

Experiment 6:
 Bacterial cells were lysed before and after progeny were formed and  progeny removed from the solution by centrifugation.
 If protein was the genetic material then there would be some transfer of S³⁵ to the progeny,if DNA P³²
Amount of S³⁵ was the same in both the early lysed sample and the late lysed sample. 
 P³² was found that there was an equal transfer of the isotope to the progeny.

Experiment 7:
 The phage coats were stripped and the concentration of S³⁵ measured. 
There was a significant decrease in the concentration of S³⁵ in the fraction with the phage progeny (from 10% to less then 1%).
The major concentration of the S³⁵ is not passed on, and thereby not involved in the creation of the progeny.


Summary:
Phage attaches to cell » P32 labeled material (DNA) enters » 80% of sulfur remains outside » progeny contain parental labeled P32!
 It was also illustrated that there the phage can be  separated  into genetic and non-genetic parts.
A final definate conclusion as to the identity of the genetic material was not possible, but the results strongly indicate DNA..

Combined with Delbruck and Luria results, this experiment went on to become a keystone in the foundation of molecular biology.
It is mainly through studies of bacteriophages that mechanisms of the genetic regulation of the vital processes have been revealed.

Questions remaining!?
What about the remaining 20% of the sulfur-labeled material? 
Does any sulfur free material from the phage enter the cell other then DNA? 
If the answer is yes, then is this material passed to the progeny?
Cannot tell if liberated DNA represents ALL DNA or only specific parts of it!
If DNA is passed on, 1 parental strain = many progeny strains, how does replication occur?


Links of Interest:
Online copy of the original paper    [PDF of Hershey & Chase 1952]
Linus Pauling and the Race for DNA
Cocktail of Nucleic Acids (yes its alcoholic!)

Questions?
email:  Heather or Matthew!

References:
Hershey, A.D. & Chase,M. (1952). Independent functions of viral protein and nucleic acid in growth of bacteriophage. Journal of General Physiology. 36:39-56

 Bio. Hershey:
http://www.nobel.se/medicine/laureates/1969/index.html
http://www.cshl.org/public/History/scientists/hershey.html
Bio. Chase:
http://osulibrary.orst.edu/specialcollections/coll/pauling/dna/index.html
http://www.biomedcentral.com/news/20030820/03

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