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X-Ray Studies of Nucleic Acids. 1947.

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Title:	X-Ray Studies of Nucleic Acids [12 of 13]
Creator:	Astbury, William
Contributor:	Symposia of the Society for Experimental Biology, No. 1
Publisher:
Date:	1947-00-00
Subject:	Nucleic acids -- Structure X-rays -- Diffraction
Description:	Symposia of the Society for Experimental Biology, No. 1
Type:	Text
Format:	text/plain
Language:	en
Identifier:	astbury-pg12
Source:	Master scanned with Epson GT-10000+ flatbed scanner at 600 dpi.
Rights:	http://osulibrary.orst.edu/specialcollections/coll/pauling/dna/copyright.html
Full Text:	X-RAY STUDIES OF NUCLEIC ACIDS 75 is between C (2) and C (3), but if that were so there would arise the situation depicted diagrammatically in Text-fig. I. The C-O bonds from C(2) and C(3) will be inclined at about the same angle to the plane of the sugar ring, and therefore the distance between successive nucleotides is defined effectively by the sum of the projections of the two O-P bonds, each I-6; A. long. Taking the O-P-O angle to be of the order of ioo°, the sum of these projections comes to little more than 21, A., a distance of approach that is far too small. One must be chary at this stage of laying down the law about almost anything pertaining to the detailed structure of the nucleic acids, but certainly if the nucleotides in the tnzv acid lie parallel and directly on top of one another, as suggested by the comparison with Na thymonucleate shown in Pl. 2, fig. j, it seems impossible for the linkage to be between C(2) and C(3) unless the bond angle subtended at the phosphorus atom becomes OH off Oil II d-ribofuranosc 2-desoiyribofuranose Text-fig. i. i 8o°, for which there is no evidence from other phosphorus compounds. If, of course, the nucleotides do not lie directly above one another, then the argument does not necessarily apply. Judging by the scale model constructed to test the proposed packing of nucleotides in Na thymonucleate, the only,,N ay of building such a column is to make use of the -CH,-011 side chain. Thus present indications are that the main internucleotide linkage in the nucleic acid from tobacco mosaic virus is between C(5) and C(3) or C(2), with slight odds in favour of C (3). I should like to express my indebtedness to Dr F. O. Bell and 1Ir L. C. Spark for the X-ray photography, to Dr k. Bailey for unfailing biochemical help, to Profs. Gulland, Caspersson, and Hammersten, and Drs Stanley and Loring, and i1Irs Beale for supplying me with specimens, and to Dr _-VI. Al. Davies for constructing atomic models. The investigation was made possible by the financial support of the Rockefeller Foundation.