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50 years of DNA

[DNA short]From the NDB. Drew, H.R., Wing, R.M., Takano, T., Broka, C., Tanaka, S., Itakura, K., Dickerson, R.E. Structure of a B-DNA Dodecamer. Conformation and Dynamics Proc. Nat. Acad. Sci. USA, 78, pp. 2179-2183, 1981.

In case you were not aware, 2003 is rather a special year in the history of crystallography as it was in the April 25, 1953 issue of Nature, that Watson and Crick published their famous paper on the structure of DNA (it is actually available free on the web as both HTML and also a pdf page-image of the original article: Many celebrations and events have been planned worldwide to celebrate this important work (if you don't believe me, type 'watson crick 50th dna' into Google, and see what you end up with!). Our New Zealand colleagues are even making the most of the fact that Maurice Wilkins was born there, although he returned to the UK with his parents at the age of 6, and never returned (see But as crystallographers, you owe it to yourself to go back to Volume 171 of Nature, and not to rely too much on the hype surrounding this anniversary. In particular, read the Watson & Crick paper (pages 737-738), and take special notice of the first sentence: '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'. Further into the brief article you will find: 'So far as we can tell, it is roughly compatible with the experimental data, but it must be regarded as unproved until it has been checked against more exact results. Some of these are given in the following communications. We were not aware of the details of the results presented there when we devised our structure, which rests mainly though not entirely on published experimental data and stereochemical arguments.'

[DNA long] Image by David S. Goodsell from the PDB’s Molecule of the Month series.

So, you will see that the famous paper on the structure of DNA, the one that introduced the elegant double helix, is really presenting little more than a hypothetical structure. No crystallographic information is presented and no crystallography experiment was reported by Watson & Crick. So why is crystallography so inextricably connected with the discovery of the structure of DNA? The answer can be found in the 'following communications' referred to by Watson & Crick. Their article is followed immediately by a paper on the 'Molecular structure of deoxypentose nucleic acids' by Wilkins, Stokes & Wilson, and that in turn is followed by a paper on 'Molecular configuration in sodium thymonucleate' by Franklin & Gosling. Although not obvious from the titles, it is these two papers that present the crystallographic evidence, not just for a helical structure, but for the actual dimensions - radius and repeat unit - that were reported by Watson & Crick. I leave it to you to decide whether the Watson & Crick structure could have been devised while being 'not aware of the details' of the crystallographic results. In line with similar meetings worldwide, the scientific program for AsCA/Crystal23 includes a session entitled 'Nucleic Acids and Their Protein Complexes (50 Years Since the Double Helix)'.

Mark Spackman exerpted from Scantz Newsletter No 54, February 03