BORON-CONTAINING OLIGODEOXYRIBONUCLEOTIDE 14MER DUPLEXES - ENZYMATIC-SYNTHESIS AND MELTING STUDIES

A set of three 14mer oligodeoxyribonucleotides of sequence d(5'-CTATGGCCTCAG*CT-3/3'-GATACCGGAGTCGA5') containing G* variants either as 2'-deoxyguanosine phosphate (unmodified), N7-cyanoborane 2'-deoxyguanosine phosphate (base-modified) or 5'-deoxyguanosine boranophosphate (backbone-modified) were synthesized by template-directed primer extension, Both the N7-cyanoborane 5'-deoxyguanosine triphosphate and 2'-deoxyguanosine alpha-boranotriphosphate nucleotides are good substrates for Sequenase, We infer that a single S-p boranophosphate linkage (which has a stereochemistry equivalent to the corresponding R(p) thiophosphate analog) is formed in the backbone-modified 14mer, Thermally induced helix-coil transitions were monitored for the hybridized duplexes using UV and circular dichroism (CD) spectroscopy, The CD spectra of the two types of boron-modified hybrids closely resemble the unmodified parent duplex, forming B-type helices in 150 mM NaCl, 1 mM EDTA, 10 mM phosphate, pH 7.4, buffer, UV melting results indicate that both hybrids have stabilities comparable with the parent duplex as measured by T-m or Delta G degrees(25). These studies indicate that singly modified base- or backbone-boronated DNA are good analogs of normal DNA.