Solution conformation of an RNA–DNA hybrid duplex containing a pyrimidine RNA strand and a purine DNA strand

International audienceRNA–DNA hybrid duplexes are involved in transcription, replication and reverse transcription of nucleic acids. Informationon such duplexes may shed some light on the mechanism of these processes. For this purpose, the influence of base compositionon the structure of a polypyrimidine–polypurine RNA–DNA duplex r(cucuccuucucuu). d(GAGAGGAAGAGAA) has beenstudied using 1H, 31P and 13C NMR experiments, molecular modeling (JUMNA program) and NOE back-calculation methods.The resulting structure of the 13-mer hybrid duplex shows that the RNA strand is in the expected A-type conformation while theDNA strand is in a very flexible conformation. In the DNA strand, the desoxyribose sugars retain the C2%-endo B-typeconformation. The duplex helical parameters (such as inclination, twist and displacement of the bases) are close to the A-typeconformation. No bending was observed for the global axis curvature. The major groove width is close to the B-form value andthe minor groove width is intermediate between standard values for A and B-forms. These results are in favour of theindependence of minor groove size (where RNase H interacts) and the base composition of the hybrid duplexes. © 2001 ElsevierScience B.V. All rights reserved