Synthetic polynucleotides and analogues as models for studies concerning DNA.

This report is divided into three topics, each of them illustrating a different use of synthetic polynucleotides and/or analogues in researches concerning DNA. In the first part, NMR studies are described where cyclic oligonucleotides are employed as important tools to improve the knowledge of the building principles of minihairpin loops. The information thus obtained has been also exploited to design stable four-way junctions from a single strand of DNA. The second part deals with the effects caused by the presence in DNA of the unusual base hmU. It appears that the substitution of the normal thymine with this base increases the local flexibility of double-stranded DNA, thus favouring the interaction with type II DNA-binding proteins (DBP II). Finally, results from various NMR investigations of complexes formed by synthetic duplexes with distamycin and analogues are presented in the last part.