Perhaps the most fascinating part of the new correspondence, however, is related to Pauling. First, Crick expressed his displeasure with the fact that Franklin might want to see Pauling on his forthcoming visit to England. “It is not impossible,” he wrote to Wilkins, “that she might consider turning over the experimental data to Pauling. This would inevitably mean that Pauling would prove the structure and not you.” To which Wilkins responded with irritation: “If Rosy wants to see Pauling, what the hell can we do about it? If we suggested it would be nicer if she didn’t that would only encourage her to do so. Why is everybody so terribly interested in seeing Pauling . . . Now Raymond [Gosling] wants to see Pauling too! To hell with it all.” This exchange is a perfect demonstration of the awe that Pauling continued to inspire even at one of the lowest moments in his career.

The April 25, 1953, issue of Nature contained three papers on the structure of DNA. First, there was the landmark paper by Watson and Crick describing the double helix structure. The paper was just a little more than one page long, but what a page that was. Watson and Crick started by acknowledging, “A structure for nucleic acid has already been proposed by Pauling and Corey. They kindly made their manuscript available to us in advance of publication.” However, they immediately added, “In our opinion, this structure is unsatisfactory.” They then concisely explained their “radically different structure,” consisting of “two helical chains each coiled around the same axis,” and, in particular, the “novel feature” of the structure, which is “the manner in which the two chains are held together by the purine and pyrimidine bases.”

Watson and Crick’s model immediately suggested a solution both to how the coding of genetic information is achieved and to the puzzle of how the molecule manages to copy itself. The details were presented in a second paper, published just five weeks after the first, in which Watson and Crick proposed the mechanism underlying the genetic code: “The phosphate-sugar backbone of our model is completely regular, but any sequence of the pairs of bases can fit into the structure. It follows that in a long molecule many different permutations are possible, and it therefore seems likely that the precise sequence of the bases is the code which carries the genetical information [emphasis added].” The message was clear: The coding of the genetic instructions that are needed to create, say, an amino acid, is contained in the specific sequence of bases in the rungs. For instance, the sequence C-G followed by G-C and then by T-A codes for forming the amino acid arginine, while G-C followed by C-G and then by T-A codes for alanine. The copying is done (precisely as anticipated abstractly by Pauling in 1948) by “unzipping” the double helix ladder at its center, producing two halves, each containing a leg and one-half of each one of the rungs. Because the sequence of bases in one chain automatically determines the sequence of the bases in the other (since the partner of T is always A, and that of G is always C), it is clear that one-half of the molecule contains all the information needed for constructing the whole molecule. For instance, if the sequence of bases along one chain of DNA is TAGCA, then the complementary sequence in the other chain must be ATCGT. This way, two new complete ladders can be generated from the original one and, hence, copying of the DNA molecule is accomplished.

In their first paper, Watson and Crick did not spell out the copying mechanism, but they remarked laconically, “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copy mechanism for the genetic material.” Crick explained later that this enigmatically economical sentence (which has been labeled “coy” by some historians of science) was, in fact, a compromise between his own desire to discuss the genetic implications in the first paper and Watson’s concern that the structure might still be wrong. The statement was, therefore, a simple claim to priority. The fact that Watson did still harbor doubts about the model is well documented in his contemporary letters.

As I have noted, two other papers in Nature accompanied the first paper by Watson and Crick. One was by Wilkins, Alexander Stokes, and Herbert Wilson, in which they analyzed some of the X-ray crystallographic data and also presented evidence that the helical structure exists not just in isolated fibers but also in intact biological systems. In the years that followed, Wilkins and his colleagues, and also Matthew Meselson, Arthur Kornberg, and others, did much work to confirm in detail the Watson and Crick model and their conclusions.