This Week's Citation Classic

After a short hiatus for vacation and a conference, This Week's Citation Classic returns with this gem from Marshall Nirenberg and Heinrich Matthaei:

Nirenberg, Marshall W., and J. Heinrich Matthaei. "The Dependence of Cell-Free Protein Synthesis in E. Coli Upon Naturally Occuring or Synthetic Polyribonucleotides." Proceedings of the National Academy of Sciences 47, 10 (October 1961): 1588-1602.

Following Oswald Avery's and Hershey and Chase's demonstration that DNA was the genetic material and Watson and Crick's solution of its structure, the race was on to determine how DNA was translated into proteins. Upstart Biochemist PI Marshall Nirenberg, fresh from a NIH postdoc in Dr. DeWitt Stetten, Jr.'s laboratory, and his first postdoc Heinrich Matthaei, conducted what was to be known as the poly-U experiment. (Many of Nirenberg's colleagues felt that it was naive for a biochemist untrained in molecular genetics to commence a brand-new area of research; at least one felt that Nirenberg was committing "professional suicide.") However, as he wrote in his laboratory notebook, Nirenberg realized that he “would not have to get polynucloetide synthesis very far to break the coding problem. Could crack life's code!”

As are many of the most important experiments in scientific history, the experiment was simple and elegant: Nirenberg and Matthaei used a mortar and pestle to grind up E. coli cells to obtain a cell-free extract. To the extract, they added a synthetic RNA, poly-uracil (UUU), and some DNase to dissolve any DNA present. The experiment used 20 test tubes, each filled with a different amino acid. For each individual experiment, 19 test tubes contained an unlabeled “cold” amino acid and one contained a "hot" radioactively tagged amino acid so they could watch the reaction. The “hot” amino acid was changed each time they did the experiment. In the experiment where the "hot" amino acid was phenylalanine, the results were "spectacular"! After an hour, the control tubes showed a background level of 70 counts per milligram of protein, whereas the "hot" phenylalanine tube showed 38,000 counts per milligram, thus demonstrating that UUU coded for phenylalanine.

In August 1961, Nirenberg presented the results to a small group of about thirty scientists at the International Congress of Biochemistry in Moscow. Francis Crick, who was among the original thirty, arranged to have Nirenberg deliver his paper again, this time to an audience of ~1000 people. It is not an exaggeration to suggest that Nirenberg and Matthaei's results were a worldwide sensation and made Nirenberg an instant scientific celebrity. For example , in January 1962, the Chicago Sun-Times announced that "No stronger proof of the universality of all life has been developed since Charles Darwin's 'The Origin of Species' demonstrated that all life is descended from one beginning. In the far future, the hope is that the hereditary lineup will be so well known that science may deal with the aberrations of DNA arrangements that produce cancer, aging, and other weaknesses of the flesh." In January 1962, Nirenberg joked to Crick, "[T]he American press has been saying that [my] work may result in (1) the cure of cancer and allied diseases (2) the cause of cancer and the end of mankind, and (3) a better knowledge of the molecular structure of God. Well, it's all in a day's work."

Nirenberg later shared the 1968 Nobel Prize with Robert Holley and Gobind Khorana.

NIH has a nice exhibit on Deciphering the Genetic Code. The photo of the vial of poly-U used in the experiment was taken from that exhibit.

Larry Moran at Sandwalk also posted on this experiment. Hopefully he will remove it now :P