N0.4356 April25,1953 NATURE 737 equipment, and to Dr. G. E. R. Deacon and the a residue on each chain every 3.4 A. in the z-direc- captain and officers of R. R.S. Discovery II for their tion. We have assumed an angle of 36between part in making the observations. at residues in the same chain, so th he 1Young, F. B., Gerrard, H., and Jevons,., Phil Mag., 40, 149 structu on each chain, that Longuet-Higglns, M.., Mon. Not. Roy. Astro. Soc., Geoph norus atom 5,285( Von Arx,. S., Woods Hole Papers in Phys. Oce (3)(1950) . Arkio. Mat. Astron. Fyeik. (Stockho Ekman, V. W., Arkiv. MOLECULAR STRUCTURE OF NUCLEIC ACIDS A Structure for Deoxyribose Nucleic Acid tog E wish t of deoxyribose n structure has novel feature biological ir A structure for proposed by Pauling their n r of tions y for s on a the ratio ibose, as e a van This figu diagr Donohue for timulated by e unpublished M. H. F. .E. Franklin and their co-workers at
738 NATURE April 25. 1953 VoL.171 King s College, London. One of us(JD. w) has been aided by a fellowship from the National Foundation for Infantile Paralysis J. D, WATSON F. E. C. crICK Medical Research Council Unit for the Study of the Molecular Structure of Biological Systems, Cavendish Laboratory, Combridge April 2 n,G. and 4 Wyatt. G. B, J. Gen, PhysioL., 36, 201 (1952) 4 Astbt ymp. Boe. Exp. BioL. 1, Nucleic Acid, 66(4 1:23mnan3,.里,Bm,经到y帅 Molecular Structure of Deoxypentose Nucleic Acids WHILE the biological properties of deoxypentose nucleic acid suggest a molecular structure con- Fig 1. Fibre diagran of de tose nucleic acid from B coh vertice taining great complexity, xray diffraction studies described here(ef Astbury) show the basic molecular the innermost maxima of each Bessel fiunction and onfiguration has great simplicity. The e of the origin The angie this line makes with the equator this communication is to describe preliminar is roughly equal to the angle between an element of ay, some of the experimental evidence for the poly. the helix and the helix axis. If a unit repeats n times nueleotide chain configuration being helical, and along the helix there will be a meridional reflexion existing in this form when in the naturel state. a (J%) on the nth layer line. The helical configuration fuller account of the work will be published shortly. produces side-bands on this fundamental frequency, The structure of deoxypentose nucleic acid is the tho effecto being to reproduce the intensity distribution alter considerably) in nucleoprotein, oxtracted or in layer line, corresponding to C in Fig. 2 ella, and in purified nucleate. The same linear group We will now briefly analyse in physical terres some f polynucleotide chains may pack togethor parallel of the effects of the shape and size of the repeat unil in different ways to give erystallinel-a, semi-crystalline or nucleotide on the diffraction pattern. First, if the or paracrystalline material. In all cases the X-ray nucleotide consists of a unit having circular symmetry diffraction photograph consists of two regions, one about an axis parallel to the helix axis, the whole determined largely by the regular spacing of nucleo- diffraction pattern is modified by the form factor of tides along the chain, and the other by the longer the nueleotide. Second, if tho nucleotide consists of pacings of tho chain configuration. The sequence of a series of points on a radius at right-angles to the different nitrogen bases along the chain is not made helix axis, the phases of radiation scatterd by the visibl helices of different diameter passing through h Oriented paracrystalline deoxypentose nucleic acid point are the same. Summation of the corresponding structure B in the followi communication by Bessel funetions gives reinforcement for the inner- Franklin and Gosling gives a fibre diagram as shown in Fig. 1(of. ref. 4). Astbury suggested that the strong 34-A. reflexion esponded to the inter nueleotide repeat along the fibre axis. The 434A layer linee, howev not due to repeat of polynucleotide composition, but to the chain con- figuration repeat, which eauses strong diffraction as the nucleotide chains have higher density than the nterstitial water, The absence of reflexions olt or near the meridian immediately suggests a structure with axis parallel to fibro length Diffraction by Helices It may be shown(also Stokes, unpublished)that the intensity distribution in the diffraction patterm of a series of points equally spaced along a helix is s of Bessel functions, A uniform continuous helix gives a series of layer lines of spacing corresponding to the helix pitch, the intensity dis tribution along the nth layer line being proportional ted along a radius tht a straight lino may be drawn approximately through lotions are plotter for an outer