A-CANONICAL AND Z-CANONICAL CONFORMATIONS IN D(CNGCGN) CRYSTALS CHARACTERIZED BY MICROFTIR AND MICRORAMAN SPECTROSCOPIES

Two crystals d (C2GCG2) and d (C5GCG5) have been studied under microsc ope by Fourier transform ir spectroscopy and Raman spectroscopy. The x -ray diffraction study of the latter crystal had shown that the d(C5GC G5) sequence is the first DNA dodecamer known to adopt a canonical A c onformation [N. Verdaguer, J. Aymami, D. Fernandez-Forner, I. Fita, M. Coll, T. Huynh-Dinh, J. Igolen, and J. A. Subirana (1991) Journal of Molecular Biology, Vol. 221, pp. 623-635]. Characteristic ir marker ba nds and Raman marker peaks of the A conformation have thus been obtain ed and are compared with previously proposed assignments correlated to fiber diffraction x-ray results obtained on polymers. The d(C2GCG2) s equence crystal had previously been studied in an intermediate form be tween B and Z [L. Urpi, J. P. Ridoux, J. Liquier, N. Verdagner, 1. Fit a, J. A. Subirana, F. Iglesias, T. Huynh-Dinh, J. Igolen, and E. Taill andier (1989) Nucleic Acids Research, Vol. 17, pp. 6669-6679]. In this paper we present results obtained from a crystal with this oligonucle otide in Z conformation. The effect of the crystallization conditions on the geometry of the obtained oligomer helix is discussed. The influ ence of the addition, to the central tetramer CGCG, of dC(n) stretches (at the 5' end) and dG(n) stretches (at the 3' end) of different leng ths, on the conformational flexibility of the nucleic acid, is conside red. (C) 1993 John Wiley & Sons, Inc.