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Hoogsteen-Paired Homopurine [R_P-PS]-DNA and Homopyrimidine RNA Strands Form a Thermally Stable Parallel Duplex

Piotr Guga, Magdalena Janicka, Anna Maciaszek, Beata Rbowska and Genowefa Nowak

Polish Academy of Sciences, Centre of Molecular and Macromolecular Studies, Department of Bioorganic Chemistry, ód, Poland

Correspondence: Address reprint requests to P. Guga, Tel.: 48-42-680-3248; E-mail: pguga{at}bio.cbmm.lodz.pl.

Homopurine deoxyribonucleoside phosphorothioates possessing all internucleotide linkages of R_P configuration form a duplex with an RNA or 2'-OMe-RNA strand with Hoogsteen complementarity. The duplexes formed with RNA templates are thermally stable at pH 5.3, while those formed with a 2'-OMe-RNA are stable at neutrality. Melting temperature and fluorescence quenching experiments indicate that the strands are parallel. Remarkably, these duplexes are thermally more stable than parallel Hoogsteen duplexes and antiparallel Watson-Crick duplexes formed by unmodified homopurine DNA molecules of the same sequence with corresponding RNA templates.