FAST COMMUNICATIONS FC9 Contributions intended for this section should be submitted to any of the Co-editors of Acta Crystallographica or Journal of Applied Crystallography. In the letter accompanying the submission authors should state why rapid publication is essential. The paper should not exceed two printed pages (about 2000 words or eight pages of double-spaced typescript including tables and figures) and figures should be clearly lettered. If the paper is available on 5.25" IBM PC compatible or 3.5" Apple~Macintosh diskettes tt would be helpful if these could be sent with the manuscript together with detail~ of the word-processing package used. Papers not judged suitable for this section will be considered for publication in the ap- propriate section of Acta Crystallographica or in Journal of Applied Crystallography. Acta Cryst. (1990.). A46, FC9-FC12 Crystal structure analysis of an A(DNA) octamer d(GTACGTAC) BY C. COURSEILLE [1 ], A. DAUTANT [1 ], M. HOSPITAL [1 ], B. LANGLOIS D'ESTAINTOT [1 ], G. PRECIGOUX [1], D. MOLKO [2] AND R. TEOULE [2] [1] Laboratoire de Cristaltographie, URA I44, CNRS, Universitd Bordeaux I, 33405 Talence, France [21 Centre d ~,tudes Nucldaires de Grenoble, 85X, F3804I Grenoble, France (Received 22 February 1990; accepted 5 March 1990) Abstract. The synthetic deoxyoctanucleotide d(GTACGTAC) crystallizes as an A-type DNA double helix. The structure has been refined to an R factor of 17% at 2.4 A resolution with 56 sol- vent molecules located. The tetragonal unit cell, space group P43212 has dimensions a=42.50 (7) and c = 24.79 (5) A. The asymmetric unit consists of a single strand of four base pairs. Introduction. Uracil does not occur as a usual component of DNA, but may appear either when dUTP residues are incorporated in place of dTTP by DNA polymerases during replication (Laval & Laval, 1970; Tye & Lehman, 1977; Lindahl, 1982), or by the in situ deamination of cytosine residues (Shapiro & Klein, 1966; Lindahl, 1979). The physiological role of correction, or repair, of deaminated cytosine residues in DNA is played by the uracil DNA glycosylase which releases a free uracil by hydrolytic cleavage of the uracil- deoxyribose bond and yields an apyrimidic site without changing the sugar-phosphate backbone (Hanawalt, Cooper, Ganesan & Smith, 1979; Lin- dahl, 1979, 1982). A few years ago, using synthetic oligonucleo- tides containing native bases (Delort, Duplaa, Molko, Teoule, Leblanc & Laval, 1985), or modi- fied bases such as m5dC (Chen, Cohen & Behe, 1983; Sanderson, Mellema, Van der Marel, Wille, Van Boom & Altona, 1983; Feigon, Wang, Van der Marel, Van Boom & Rich, 1984; Prettre- Giessner, Pullman, Tran-Dinh, Neumann, Huynh-Dinh & lgolen, 1984; Taboury, Adam, 0108-7673/90/04FC009-0453.00 Taillandier, Neumann, Tran-Dinh, Huynh-Dinh, Langlois d'Estaintot, Conti & lgolen, 1984), 2- amino dA (Taboury et al., 1984), m6dA (Fazaker- ley, Teoule, Guy, & Gushlbauer, 1984) it was shown, by enzymatic processes (Delort, Duplaa et at., 1985) and 1H NMR or other spectroscopic analyses (Chen et al., 1983; Sanderson et al., 1983; Fazakerley et at., 1984; Feigon et at., 1984; Prettre-Giessner et al., 1984) that the excision of the uracil is not a random phenomenon. The se- quence of the bases surrounding the uracil has an influence on the rate of excision (Delort, Duplaa et at., 1985). Some 1H NMR studies carried out on d(GTACGTAC) and d(GTACGUAC) showed that the introduction of a uracil in place of a thymine does not affect the global structure of DNA and, therefore, that the recognition of the uracil defect by uracil-DNA glycosylase was not based upon a bulky distorsion (Delort, Neumann, Molko, Herv6, Teoule & Tran-Dinh, 1985). Precise details on the conformation of these oli- gonucleotides can come only from single-crystal X-ray studies, thus we undertook the crystalliza- tion experiments and structure resolution of the native d(GTACGTAC). Materials and methods. The oligomer d(GTACGTAC) was synthesized by phosphor- amidite methodology on an Applied Biosystems synthesizer (381A). Complete cleavage and de- protection was carried out following standard procedures and the crude material was purified © 1990 International Union of Crystallography