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Letter from James Watson to Linus Pauling. March 4, 1963.
Watson writes to explain the background behind his and Crick's earlier assumption of the existence of two hydrogen bonds linking cytosine and guanine in the DNA molecule. Watson then confirms that he and Crick have accepted the Pauling-Corey description of three hydrogen bonds interlinking cytosine and guanine.


REC’D MAR 5 1963





March 4, 1963

Dr. Linus Pauling

Gates and Crellin Laboratories of Chemistry

California Institute of Technology

Pasadena 1, Calif.

Dear Dr. Pauling,

After Jerry Donohue told us that guanine and uracil would be Keto, I made metal models of the bases using published values when available an otherwise making likely guesses. Then I suspected Broomhead’s guanine structure was not correct in detail (in particular the angle of the Keto oxygen) but nonetheless I used her bond angles and lengths. Its effect was to make formation of three good hydrogen bonds unlikely (the 3rd was too long). So we settled for two leaving open the question whether a refined guanine structure would imply 3 bonds. To my knowledge both Francis and I have accepted the probable existence of 3 good bonds ever since the appearance of your manuscript with Dr. Corey. Now a student of Alex Rich is completing the structure of a mixed (1:1) guanine-cytosine crystal. He finds three strong hydrogen bonds confirming your analysis. Why the “Scientific American” left out ht e3rd bond Is not known to me but I suspect an oversight.

I enclose a copy of my Nobel lecture. It covers my interest in protein synthesis. The DNA structure is treated in Wilkins’ lecture. Crick spoke on the “Code”.

With best regards to your wife and to Linda.

James D. Watson



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