Transcription factors represent only a small fraction of the proteins in a cell. Link to a discussion of how they can nonetheless be isolated and purified. Hormones exert many of their effects by forming transcription factors. The complexes of hormones with their receptor represent one class of transcription factor. Link to a discussion of these.
Embryonic development requires the coordinated production and distribution of transcription factors.
Link to a discussion of some of the transcription factors that produce the segmented body plan in Drosophila. Binding increases the rate of transcription of the gene. Enhancers can be located upstream, downstream, or even within the gene they control. These are bound by an enhancer-binding protein designated E2 . 1860 base pairs of DNA between the two.