Figure 1. Structure of (a) the yeast GCN4 factor and (b) the mammalian glucocorticoid receptor, indicating the distinct regions that mediate DNA binding or transcription activation.

Figure 2. Potential mechanisms by which a transcription factor can repress gene expression. This can occur: (a) by the repressor (R) producing a tightly packed chromatin structure which prevents an activator (A) from binding; (b) by the repressor binding to the DNA-binding site of the activator and preventing it from binding and activating gene expression; (c) by the repressor interacting with the activator in solution and preventing its DNA binding; (d) by the repressor binding to DNA with the activator and neutralizing its ability to activate gene expression or (e) by direct repression by an inhibitory transcription factor. ABS: activator-binding site.

Figure 3. Gene activation mediated by (a) the synthesis of a transcription factor only in a specific tissue or (b) activation of the transcription factor only in a specific tissue.

Figure 4. Mechanisms by which transcription factors can be activated by posttranslational changes. The circle represents an active transcription factor, while the square represents a nonactive factor. The open box represents either an inhibitory protein or a portion of the factor, which has been cleaved off in the process of activation. L: ligand; P: phosphorylation.