TEMPERATURE AND SALT DEPENDENCE OF HIGHER-ORDER STRUCTURE FORMATION BY ANTISENSE C-MYC AND C-MYB PHOSPHOROTHIOATE OLIGODEOXYRIBONUCLEOTIDESCONTAINING TETRAGUANYLATE TRACTS

The use of complementary RNA or DNA sequences to selectively interfere with the utilization of mRNA of a target gene is an attractive therap eutic strategy. Two well-studied targets for oligonucleotide therapy a re the c-myc and c-myb proto-oncogenes. It has been reported that sequ ences which contain four contiguous Gs can elicit a non-antisense resp onse, due to the formation of a homotetrameric G quartet structure. Th erefore, it was of interest to determine whether anti-c-myc and anti-c -myb phosphorothioate DNAs including tetraguanylate form higher order structures under physiologically relevant salt conditions and temperat ure. First, the identity of the higher order structure was established and was found to be a tetraplex, Employing intracellular (high K+), e xtracellular (low K+) and normal saline (no K+) salt mixtures, native gel electrophoresis revealed no tetraplex formation at 37 degrees C, t he physiologically relevant temperature, On the other hand, tetraplex structure formation was observed at 4 and 23 degrees C, Hence, the pot ential for these sequences to form tetraplex structures at lower tempe ratures may not be relevant for their activity in cells and animals at physiological temperature.