Nucleic Acids Research, 1990, Vol. 18, No. 6 1559-1564
© 1990
MOLECULAR BIOLOGY |
DNA with adenine tracts contains poly(dA).poly(dT) conformational features in solution
Institut Jacques Monod, CNRS, Universite Paris VII Tour 43 2 Place Jussieu, 75251 Paris Cedex 05, France
Received November 2, 1989. Revised January 4, 1990. Accepted January 4, 1990.
The conformation of DNA's with adenine-thymine tracts exhibiting retardation in electrophoretic migration and considered as curved were investigated in solution by CD and RAMAN spectroscopy. The following curved multimers with adenine tracts but of different flanking sequences d(CA5TGCC)n, d(TCTCTA6TATATA5)n, d(GA4T4C)n yield CD spectroscopic features indicating a non-B structure of the dA.dT tract with similarities to polyd(A).polyd(T). We suggest that adenine-thymine bases in these multimers contain some of the distinctive conformational features of polyd(A).polyd(T) probably with large propeller twist found by NMR (Behling and Kearns, 1987) and by X-ray diffraction on oligonucleotides containing a tract of adenines (Nelson et al. 1987, Coll et al; 1987; DiGabriele et al. 1989). Some elements of distinctive CD features of the contiguous adenines run are also observed in the straight multi-9-mer d(CA5GCC)n which lacks in-phase relation to the helical repeat. Despite the presence of the TpA step in the straight multimer d(GT4A4)n, the altered dA.dT conformation is not completely destroyed. Interruption of adenine tract by a guanlne in d(CAAGAATGCC)n leads to a B-like conformation and to a normal electrophoretic mobility. The Raman spectra reveal a rearrangement of the sugar-phosphate backbone of dA.dT tract in the multimer d(CA5TGCC)n with respect to that of polydA.polydT. This is reflected in the presence of an unique Raman band associated to C2'-endo sugar with a predominant contribution of C1'-exo puckering which is exhibited by the multimer whereas two distinct Raman bands characterize poly(dA).poly(dT) backbone conformation.
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