Determination of the melting temperature of oligonucleotide duplexes RNA oligonucleotide 18RNA (5 0 GCGCGCUGGAGGC CAUGG3 0 , Dharmacon, USA) was mixed in a 1:1 molar ratio with RNA18, DNA18 or one of the various DNA/ LNA mix-mers, in UV-melting buffer (100 mM NaCl, 10 mM Cacodylate acid, pH 6.8). The analysis was performed on a Varian Cary 300 spectrophotometer using temperature ramps of 0.25 C /min during heating and cooling. The absorbance at 260 nm was recorded and normalized to the blank control.