Strategies for inhibiting transcription. (A) Homologous recombination. Cross-over exchange between the targeting vector and genomic material during cell division is indicated. See text for more detailed explanation of events. (B) Triple-helix formation in the major groove between a polypyrimidine oligodeoxynucleotide (open pattern line) and polypurine sequence in double-stranded (black line) DNA. Textural representation of this event is indicated below the cartoon. (C) Decoy strategy. Double-stranded oligonucleotides compete with the native binding site for transcription factor protein (dark globular structures).