Hershey & Chase

D. Hershey & Chase

    Alfred D. Hershey went to Michigan State College to get his B.S. in 1930 and his PhD in 1934. In 1967, he got an honorary D.Sc. at the University of Chicago. From 1934 to 1950 he was engaged in teaching and research, at the Department of Bacteriology, Washington University School of Medicine. Martha Chase is an American scientist who was a geneticist and part of the team that showed DNA rather than protein is the genetic material of life. She earned her bachelor's degree from the College of Wooster in 1950 and her PhD from the University of Southern California in 1964


They thought that since no dilution had occurred from an osmotic shock then the particles had an osmotic membrane.They interpreted that inner cellular DNA. Derived from phage is not merely DNA in a solution but is part of an organized structure at all times during the latent period. 


    Glycerol lactate was used to permit growth of bacteria without undesirable pH changes at low concentrations of sulfur and phosphorus.They resulted in plentiful bacteria as many as 2 times 10 to the 9th power per square ml. To prove that their principle findings reflect genuine properties of viable phage particles they relied on some experiments of inactive phage.


    When a particle of bateriophage T2 attaches to a bacterial cell, most of the phage DNA enters the cell, and a residue containing at least 80 per cent of the sulfur-containing protein of the phage remains at the cell surface. This residue consists of the material forming the protective membrane of the resting phage particle, and it plays no further role in infection after the attachment of phage to bacterium. Their experiments show that there is clearly a physical separation of the phage T2 into genetic and non-genetic parts is possible. A corresponding functional separation is seen in the partial independence of phentoype and genotype in the same phage.


    Osmotic shock disrupts particles of phage T2 into material containing nearly all the phage sulfur in a form precipitable by antiphage serum, and capable of specific adsorption to bacteria. Adsorption of T2 to heat-killed bacteria, and heating or alternate freezing and thawing of infected cells, sensitize the DNA of the adsorbed phade to DNase. Adsorption of phage T2 to bacterial debris causes part of the phage DNA to appear in solution, leaving the phage sulfur attached to the debris. Suspensions of infected cells agitated in the Waring blendor release 75 per cent of the phage sulfur and only 15 per cent of the phage phosphorus to the solution as a result of the applied shearing force. The facts stated show that most of the phage sulfur remains at the cell surface and most of the phage DNA enters the cell on infection. Whether sulfur-free material other than DNA enters the cell has not been determined. The phage progeny yielded by bacteria infected with phage labeled with radioactive sulfur contain less than 1 per cent of the parental radioactivity. Phage inactivated by dilute formaldehyde is capable of adsorbing to bacteria, but does not release its DNA to the cell. The sulfur-containing protein of resting phage particles is confined to a protective coat that is responsible for the adsorption to bacteria, and functions as an instrument for the injection of the phage DNA into the cell.