Nucleic Acids Research, 2001, Vol. 29, No. 23 4873-4880
© 2001 Oxford University Press
Triplex formation by morpholino oligodeoxyribonucleotides in the HER-2/neu promoter requires the pyrimidine motif
Arizona Cancer Center, University of Arizona, 1515 North Campbell Avenue, Tucson, AZ 85724-5024, USA and 1James Graham Brown Cancer Center, Department of Medicine, University of Louisville, Louisville, KY, USA
Triplex-forming oligonucleotides (TFOs) are good candidates to be used as site-specific DNA-binding agents. Two obstacles encountered with TFOs are susceptibility to nuclease activity and a requirement for magnesium for triplex formation. Morpholino oligonucleotides were shown in one study to form triplexes in the absence of magnesium. In the current study, we have compared phosphodiester and morpholino oligonucleotides targeting a homopurinehomopyrimidine region in the human HER2/neu promoter. Using gel mobility shift analysis, our data demonstrate that triplex formation by phosphodiester oligonucleotides at the HER-2/neu promoter target is possible with pyrimidine-parallel, purine-antiparallel and mixed sequence (GT)-antiparallel motifs. Only the pyrimidine-parallel motif morpholino TFO was capable of efficient triple helix formation, which required low pH. Triplex formation with the morpholino TFO was efficient in low or no magnesium. The pyrimidine motif TFOs with either a phosphodiester or morpholino backbone were able to form triple helices in the presence of potassium ions, but required low pH. We have rationalized the experimental observations with detailed molecular modeling studies. These data demonstrate the potential for the development of TFOs based on the morpholino backbone modification and demonstrate that the pyrimidine motif is the preferred motif for triple helix formation by morpholino oligonucleotides.
* To whom correspondence should be addressed. Tel: +1 520 626 3424; Fax: +1 520 626 3754; Email: sebbinghaus{at}azcc.arizona.edu
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