SYNTHESIS AND BASE-PAIRING PROPERTIES OF THE NUCLEASE-RESISTANT ALPHA-ANOMERIC DODECARIBONUCLEOTIDE ALPHA-[R(UCUUAACCCACA)]

The non natural oligoribonucleotide alpha-[r(UCUUAACCCACA)] consisting exclusively of alpha-anomeric ribonucleoside units was synthesized according to the phosphoramidite methodology and the solid support technology. For this purpose, the base-protected alpha-ribonucleosides were synthesized and converted into their O-methylphosphoramidites. Assembling was carried out on a DNA synthesizer with an average efficiency of 97% per step. Base composition of this nuclease-resistant alpha-RNA strand was ascertained after chemical and enzymatic hydrolysis and HPLC analysis of the hydrolysate. Whereas no spectroscopic evidence of base pairing was found above 0-degrees-C between alpha-[r(UCUUAACCCACA)] and beta-[d(TGTGGGTTAAGA)], a clear UV absorbance transition (Tm 25.5-degrees-C) was observed during the hybridization of the same alpha-RNA strand with beta-[d(AGAATTGGGTGT)]. In this latter case, the mixing curve titration suggests formation at low temperature of a triplex involving two alpha-RNA and one beta-DNA strands. Moreover, this alpha-decaribonucleotide complementary in parallel orientation of the splice receptor of HIV-1 tat mRNA was found to inhibit (10-mu-M < ED50 < 20-mu-M), with apparent lack of sequence specificity, the de novo HIV-1 infection in cultured cells.