Characteristics of the major transcription factor classes.

Transcription factors (TFs) share the generic property of binding to specific DNA sequences (which are often palindromic so the binding of both strands can occur in antiparallel ways). But each family of TFs varies in detail in how its DNA binding is accomplished. Scheme 7-3 shows some of the major mechanisms (this section is not exhaustive but again is intended to suggest the modular nature and logic of the process and the diversity of agents that bring it about).

Scheme 7-3. DNA binding motifs. Helix-turn-helix motif; (A) homeodomain bound to its specific DNA sequence; (B) specific amino acids of helix 3 (recognition helix) make contact with the major groove of the target DNA at specific sites; (C) zinc-finger motif: this motif uses zinc fingers of specific amino acids to recognize DNA binding sites; (D) leucine zipper motif; two a-helical DNA-binding domains join to form a leucine zipper dimer that binds to a specific DNA sequence.

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