Triple-helices targeted to the polypurine tract of a murine retrovirus.

The all-purine 13-mer oligodeoxyribonucleotide d(GGGGGGAAAAAGA), containing an unusually large block of contiguous guanines, was shown by electrophoresis and thermoelution to form a specific, 'antiparallel' complex with the duplex containing the polypurine tract of murine retroviruses. Fourier transform infra-red spectroscopy (FTIR) and molecular modeling indicated that the complex is based on reverse Hoogsteen G(GC) and A(AT) triplets, with anti orientations of the bases and with all the strands having S-type sugar conformations. This G + A-containing 13-mer and a G + T-containing 22-mer, d(TGTTTGTTTGGGGGGTTTTTGT), aimed at the same target, retarded in a sequence-specific manner the spreading of the Friend retrovirus in Dunni cells infected de novo, thus indicating that the polypurine tract of retroviruses may be a suitable target for anti-gene action.