WHY PENTOSE-NUCLEIC AND NOT HEXOSE-NUCLEIC ACIDS .3. OLIGO(2',3'-DIDEOXY-BETA-D-GLUCOPYRANOSYL)NUCLEOTIDES - (HOMO-DNA) - BASE-PAIRING PROPERTIES

The paper presents results of a comprehensive investigation on the pairing properties of homo-DNA oligonucleotides, the preparation of which has been described in Part II of this series [2]. The investigation was carried out by using established methods described in the literature for the characterization of oligonucleotides in the natural series, such as determination of melting temperatures of oligonucleotide duplexes by temperature-dependent UV spectroscopy, determination of thermodynamic data of duplex formation from the concentration dependence of melting temperatures, determination of pairing stoichiometry by ratio-dependent UV spectroscopy of binary mixtures of pairing partners, temperature-dependent CD spectroscopy, gel electrophoresis under non-denaturing conditions, and - in selected cases - H-1- and P-31-NMR spectroscopy. The systematic comparison of the paring properties of homo-DNA oligonucleotides with corresponding DNA nucleotides (up to dodecamers) indicates that homo-DNA is a highly efficient, autonomous, artificial pairing system with a pairing behavior that is in part similar to, but also, in part, strikingly different from, the pairing behavior of DNA. The pairing properties established so far are listed below in a manner that reflects the sequence of subtitles in Chapt. 2 of the text; they were determined under the conditions: H2O, 0.15m NaCl, 0.01m Tris-HCl buffer, pH 7, oligonucleotide concentrations in the mum range, 1:1 ratio of single strands in the case of non-selfcomplementary sequences.