Figure 1.

Transcription regulatory networks provide models to understand differential gene expression at a systems level. Transcription regulatory networks are composed of two types of components, or nodes: the genes involved in the system and the TFs that regulate their expression. Protein-protein interactions between TFs and protein-DNA interactions between TFs and their target genes can be visualized in transcription regulatory networks. The dashed line represents TF-TF protein-protein interaction (heterodimer). Arrows represent protein DNA interactions that result in transcription activation; the blunt 'arrow' represents protein-DNA interaction that results in repression of transcription.