Thursday, April 25, 2013

Sixty Years Ago Today: April 25, 1953

Sixty years ago on this day, Nature published three back-to-back papers on the structure of DNA. It was a momentous day for science. Here's how Horace Judson describes it in The Eighth Day of Creations (pp. 154-155)...
The letter to Nature appeared in the April 25 issue. [It was submitted on April 2—LAM] To those of its readers who were close to the questions, and who had not already heard the news, the letter must come off like a string of depth charges in a column sea. "We wish to suggest a structure for the salt of deoxyribose nucleic acid (D.N.A.). This structure has novel features which are of considerable biological interest," the letter began; at the end, "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material." That last sentence has been called one of the most coy statements in the literature of science. According to Watson, Crick wrote it. Wilkins's paper followed, signed also by two of his associates at King's College, A. R. Stokes and H. R. Wilson. It was a restatement of helical diffraction theory, and sprang to life and significance only in the last paragraphs, where Wilkins briefly reported that his x-ray diffraction studies of intact sperm heads and bacteriophage—both, of course, containing a high proportion of DNA—gave patterns that suggested that DNA in living creatures has a helical structure similar to the model just proposed. The note by Franklin and Gosling came next. It was a revision and extension of their draft from the middle of March, in the light of the model. It presented the crucial diffraction photo structure B and analyze that and the other experimental evidence to show—with curt authority—that Franklin's data were compatible with Watson and Crick's structure.
The three papers are ....

Watson, J.D. and Crick, F.H.C. (1953)A Structure for Deoxyribose Nucleic Acid. Nature 171:737-738. [See: The Watson & Crick Nature Paper (1953)] [PDF]
"We wish to suggest a structure for the salt of deoxyribose nucleic acid (D.N.A.). This structure has novel features which are of considerable biological interest."

Wilins, M.H.F., Stokes, A.R., and Wilson, H.R. (1953) Molecular Structure of Deoxypentose Nucleic Acids. Nature 171:738-740. [See: The Wilkins, Stokes and Wilson Nature paper (1953)] [PDF]
"The biological significance of a two-chain nucleic acid unit has been noted (see preceding communication). The evidence that the helical structure discussed above does, in fact, exist in intact biological systems is briefly as follows: ..."

Franklin, R. and Gosling, R.G. (1953) Molecular Configuration in Sodium Thymonucleate. Nature 171:740-741. [See: The Franklin & Gosling Nature paper (1953)] [PDF]
"Thus, while we do not attempt to offer a complete interpretation of the fibre-diagram of structure B, we may state the following conclusions. The structure is probably helical. The phosphate groups lie on the outside of the structural unit, on a helix of diameter about 20 Å. The structural unit probably consists of two co-axial molecules which are not equally spaced along the fiber axis, their mutual displacement being such as to account for the variation of observed intensities of the innermost maxima on the layer lines; if one molecule is displaced from the other by about three-eights of the fibre-axis period, this would account for the absence of the fourth layer line maxima and the weakness of the sixth. Thus, our general ideas are not inconsistent with the model proposed by Watson and crick in the preceding communication."