|A Very Pretty Model
When Watson told Wilkins of Pauling's mistake and his idea that DNA was helical, he
was given a reward: his first look at the most recent x-ray patterns Franklin had
gotten from the molecule. She had confirmed that DNA existed in two forms, a condensed
dry form and an extended wet form the structure assumed when it drank up all that
water. Astbury's photos, the ones Pauling had used, had been of a mixture of the two
forms. Franklin's recent shots, much clearer and of only the extended form, immediately
confirmed to Watson that the molecule was a helix. It also gave him several new parameters
for its solution.
Pauling had already moved on to new projects - a theory of ferromagnetism and plans
for a major international protein conference in Caltech the next fall - when Peter
wrote him in mid-February about the English were critical of his DNA structure. "I
am checking over the nucleic acid structure again, trying to refine the parameters
a bit," Pauling wrote back. "I heard a rumor that Jim Watson and Crick had formulated
this structure already sometime back, but had not done anything about it. Probably
the rumor is exaggerated."
But Pauling sensed that something was very wrong. When he gave a seminar on his DNA
structure at Caltech, the reception was cool; afterward, Delbrück told a colleague
that he thought Pauling's model was not convincing. He mentioned a letter he had gotten
from Watson saying that Pauling's structure contained "some very bad mistakes" and
in which Watson had added, "I have a very pretty model, which is so pretty that I
am surprised that no-one ever thought of it before."
Pauling wanted to know more. He quickly wrote Watson, inviting him to his fall protein
conference, mentioning that he had heard from Delbrück about his DNA work, and encouraging
him to keep working on the problem. "Professor Corey and I do not feel that our structure
has been proven to be right," he wrote, "although we incline to think that it is."
Crick's barb about what held the molecule together led him to gather chemical precedents
for the existence of adjoining negative charges in the same molecule, and he began
to reason to himself that perhaps the DNA core environment was a special one that
allowed the phosphates to exist as he had proposed. Meanwhile, Todd had sent him the
requested samples of nucleotides, and Pauling started their x-ray analysis. He was
finally laying the groundwork for a reasonable structure. But it was too late.