The Hershey Chase Expt

    A very common type of virus that infects only E. coli is one called "T4," which consists only of a protein capsid, and a core of DNA. This leads us to think of a very elegantly simple experiment. This should conclusively show us that protein is the genetic material and not DNA.

    DNA consists of only four different monomers - a situation of highly limited coding ability. Proteins with their twenty different monomers (amino acids) hold astronomically greater coding potential.

    We thus took this other lab's finding and applied it to our problem.

    We took another non-radioactive culture of E. coli, and dumped in some of our doubly-labelled T4. We immediately began taking samples every minute, and put those samples in a blender hoping that the turbulence would be able to rip the residual T4 off of the bacterial cell surfaces. Even small amounts of protein genes the phage direct to go into the cell should be found with the cells and not in the soluble ripped-away phage supernate. Remember that after centrifuging down the cells - the ripped-off phages would be too small to centrifuge down easily. Then we can test both the overlying supernates and the cellular pellets at the bottom of the tubes for which isotopes were present.

    These two graphs show an astounding finding. You see that none of the S-35 is associated with the bacterial pellet, but only that tritium is! The tritium disappears into the bacteria in a matter of only a few minutes. This can only mean that all of us who thought that protein must be the genetic material have been wrong, and that, instead, it is the simple DNA that is. The simplicity of DNA's make-up has us in a real quandary! DNA must be more complicated that we have been thinking.