The potential for gene repair via triple helix formation

Abstract

Triplex-forming oligonucleotides (TFOs) can bind to polypurine/polypyrimidine regions in DNA in a sequence-specific manner. The specificity of this binding raises the possibility of using triplex formation for directed genome modification, with the ultimate goal of repairing genetic defects in human cells. Several studies have demonstrated that treatment of mammalian cells with TFOs can provoke DNA repair and recombination, in a manner that can be exploited to introduce desired sequence changes. This review will summarize recent advances in this field while also highlighting major obstacles that remain to be overcome before the application of triplex technology to therapeutic gene repair can be achieved.

Figure 1

Diagrammatic depiction of a DNA triple helix, with the third strand binding in the major groove.

Figure 2

Diagram of the pyrimidine motif for triple helix formation. (a) Orientation of the third strand in the pyrimidine triple-helix motif. Note that the third strand is parallel in terms of 5′ to 3′ orientation with respect to the purine-rich strand of the duplex target. (b) Base triplets formed in the pyrimidine motif and illustration of the Hoogsteen hydrogen bonds that stabilize triple-helix formation.

Figure 3

Diagram of the purine motif for triple-helix formation. (a) Orientation of the third strand in the purine triple-helix motif. Note that the third strand is oriented antiparallel in terms of 5′ to 3′ direction with respect to the purine-rich strand of the duplex target. (b) Base triplets formed in the purine motif and illustration of the reverse Hoogsteen hydrogen bonds that stabilize triple-helix formation.