The Hershey-Chase food blender

Hershey-Chase blenderShould you ever visit Cold Spring Harbor Laboratory on Long Island, New York, be sure to go see the food blender that was used to carry out the well known Hershey-Chase experiment. The blender is located in the Szybalski Reading Room of the Carnegie Library. After entering the front door of the library, walk straight back, enter the Szybalski Room, and turn right to find the blender in a display case.

At left is a photograph of the blender, partially hidden behind a letter (click the photo for a larger view). You can see the cap of the blender and the main body into which liquids are poured. I presume the motor is hidden from view. Behind the blender is a diagram of the Hershey-Chase experiment.

The letter is also worth reading because it concerns salary negotiations between Hershey and Milislav Demerec, who was the President of Cold Spring Harbor Laboratory from 1940 to 1960 (at that time it was called the Carnegie Institute of Washington). The letter is dated 15 January 1950 and was written while Hershey was at Washington University in St. Louis, MO:

Dear Dr. Demerec:

I have decided that I would like to come to Cold Spring Harbor, provided we can agree about salary. Carnegie is my first choice, but I do not feel that I can make an appreciable monetary sacrifice in its favor. I still do not know what will be done for me here, of course, but I think we can assume that it will be inferior in one way or another to the prospects at Illinois.

I believe I told you that the offer from Illinois was a professorship at $7000. This is the basic salary for nine months, to which is added $1500 if I teach a course in summer school. One can, of course, also supplement income by teaching elsewhere in the summer, as Luria is doing in Colorado this year. In a telephone conversation this morning, Dr. Spiegelman* told me that Dr. Halvorson is willing to go to the administration with my request for a basic salary of $8000, but wants first to have some assurance that I will accept on those terms. I am therefore writing to you first.

Under these circumstances, I feel that the minimum I can accept is $8000. I hope very much that you will be willing to consider this amount.

The letter is interesting not only because of the $8000 yearly salary that Hershey requests, low by today’s standards, but also his candor in writing to Demerec.

In front of the letter is a photograph of Al Hershey in the laboratory. On This Week in Microbiology #40 Waclaw Szybalski noted that Hershey was not happy when his experiments did not work. In the photo he is pipetting and looking very serious; I wonder what was the outcome of that experiment.

Chase letterAlso in the case is a brief handwritten note from Hershey to Demerec written on 12 June 1950:

Dear Demerec,

I shall be very glad to have Ms. Chase if she decides to accept.

Yours, Hershey

Martha Chase of course did become Hershey’s laboratory assistant.

*Sol Spiegelman was on the faculty of the University of Illinois and presumably was attempting to recruit Hershey. Years later Spiegelman was a Professor at Columbia University. In 1982 he interviewed me for a faculty position in the Department of Microbiology. He was instrumental in obtaining extra start-up funds for my laboratory to match other offers that I had obtained. He recruited me to Columbia but he could not attract Hershey to Illinois.

From a food blender to real-time fluorescent imaging

single phage infectionAlthough Avery, MacLeod, and McCarty showed in 1944 that nucleic acid was both necessary and sufficient for the transfer of bacterial genetic traits, protein was still suspected to be a critical component of viral heredity. Alfred Hershey and Martha Chase showed that this hypothesis was incorrect with a simple experiment involving the use of a food blender. The Hershey-Chase conclusion has since been upheld numerous times*, the most recent by a modern-day experiment using real-time fluorescence.

Hershey and Chase made preparations of the tailed bacteriophage T2 with the viral proteins labeled with radioactive sulfur, and the nucleic acids labeled with radioactive phosphorus. The virions were added to a bacterial host, and after a short period of time were sheared from the cell surface by agitation in a blender. After this treatment, the radioactive phosphorus, but not the radioactive sulfur, remained associated with bacterial cells. These infected cells went on to produce new virus particles, showing that DNA contained all the information needed to produce a bacteriophage.

In a modern validation of the Hershey-Chase experiment, bacteriophages are mixed with a cyanine dye which binds to the viral DNA (illustrated). Upon infection of the bacterial host, the phage DNA is injected into the cell together with the dye. In time the dye leaves the phage DNA and binds to the host genome. This process can be observed in real-time (as it happens) by fluorescence microscopy.

This technique was used to visualize single bacteriophages infecting an E. coli host cell. It takes about 5 minutes on average for 80% of bacteriophage lambda DNA to exit the capsid, with a range of 1-20 minutes.

These experiments do not simply provide a visual counterpart to the Hershey-Chase conclusion, but reveal additional insights into how viral DNA leaves the capsid. One interesting observation is that the amount of DNA that remains in the capsid apparently is not the sole determinant of how quickly ejection occurs. The amount of DNA ejected from the capsid does appear to regulate the dynamics of the process.

The kitchen blender experiment contrasts vividly with the complexity of real-time fluorescent imaging. Hershey and Chase did not have the technology to visualize phage DNA entering the host cell; they used what was available to them at the time. While improved technology is important for pushing research forward, simple experiments will always make important contributions to our understanding of science.

*The infectivity of cloned viral DNA is one validation of the Hershey-Chase experiment.

Hershey, AD, Chase, M. 1952. Independent functions of viral protein and nucleic acid in growth of bacteriophage. J. Gen. Physiol. 36:39-56. 

Van Valen, D., Wu, D., Chen, Y-J, Tuson, H, Wiggins, P, Phillips, R. 2012. A single-molecule Hershey-Chase experiment. Current Biol 22:1339-1343.