A Twist Of Fate

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Wilkins was intrigued; the pictures convinced him more firmly than ever that the DNA molecule was helical, and he proposed to collaborate with Franklin in exploring the B form in detail. But Franklin, who still thought there was no evidence of a helix in her pictures, went into a rage, according to Wilkins. "She exploded," writes Brenda Maddox in her sympathetic 2002 biography Rosalind Franklin: The Dark Lady of DNA. "Rosalind had good reason... Undervalued at King's, she had just achieved extraordinary results by working in virtual isolation. Now what she saw as a less able colleague of higher rank was proposing to elbow in and spoil the clarity of her investigation." Alarmed by what had become a very public quarrel, lab director Randall declared that from now on Wilkins would work with the B form of DNA and Franklin would have exclusive rights to the A form. Unwittingly and indirectly, he had just handed Watson and Crick a crucial piece of information.

Through the summer and fall of 1952, Watson and Crick kept talking, trying to fit together the still unconnected pieces of the DNA puzzle. One piece was a discovery that had been made years earlier by the Austrian refugee Erwin Chargaff. Analyzing the DNA of many different organisms, he found that while the overall proportions of the four DNA bases varied among species, the number of adenine molecules always equaled the number of thymine, and guanine and cytosine were similarly matched. (Chargaff visited Cambridge during this period and was appalled at how little basic chemistry Watson and Crick knew--and offended by how little this seemed to bother them.)

But progress on the greater problem was slow. "On a few walks our enthusiasm would build up to the point that we fiddled with the models when we got back to our office," writes Watson. "But almost immediately Francis saw that the reasoning which had momentarily given us hope led nowhere... Several times I carried on alone for a half hour or so, but without Francis' reassuring chatter my inability to think in three dimensions became all too apparent."

In December 1952, they got some bad news. In a letter to his son Peter, then a graduate student at Cambridge, Pauling revealed that he would soon publish a paper on the structure of DNA. It looked as if Watson and Crick had lost the race. Peter received his father's paper on Jan. 28 and walked into Watson and Crick's office to tell them about it. "Giving Francis no chance to ask for the manuscript," writes Watson, "I pulled it out of Peter's outside coat pocket and began reading." The senior Pauling had come up with a three-stranded molecule with the sugar-phosphate backbone at the center. Almost immediately, Watson realized it didn't make sense. "I could not pinpoint the mistake, however, until I looked at the illustrations for several minutes. Then I realized that the phosphate groups in Linus' model were not ionized... Pauling's nucleic acid in a sense was not an acid at all."