Gene expression may be disrupted, as indicated by the “X,” at the level of transcription, or translation. Oligonucleotides can inhibit transcription (1) by triple-helix formation with chromosomal DNA, or by acting as decoy's for transcription factors (see Fig 2). Hybridization of an oligonucleotide to mRNA may inhibit translation (2) by hindering the ability of the ribosome complex to “read” the mRNA sequence, or by providing a substrate for RNase H (see Fig 3).