C. Escude et al., STABLE TRIPLE HELICES FORMED BY OLIGONUCLEOTIDE N3'-]P5' PHOSPHORAMIDATES INHIBIT TRANSCRIPTION ELONGATION, Proceedings of the National Academy of Sciences of the United Statesof America, 93(9), 1996, pp. 4365-4369
Oligonucleotide analogs with N3' --> P5' phosphoramidate linkages bind
to the major groove of double-helical DNA at specific oligopurine oli
gopyrimidine sequences. These triple-helical complexes are much more s
table than those formed by oligonucleotides with natural phosphodieste
r linkages. Oligonucleotide phosphoramidates containing thymine and cy
tosine or thymine, cytosine, and guanine bind strongly to the polypuri
ne tract of human immunodeficiency virus proviral DNA under physiologi
cal conditions. Site-specific cleavage by the Dra I restriction enzyme
at the 5' end of the polypurine sequence was inhibited by tripler for
mation. A eukaryotic transcription assay was used to investigate the e
ffect of oligophosphoramidate binding to the polypurine tract sequence
on transcription of the type 1 human immunodeficiency virus nef gene
under the control of a cytomegalovirus promoter. An efficient arrest o
f RNA polymerase II was observed at the specific tripler site at submi
cromolar concentrations.