Transcription factors are modular in structure means constructed with standardized units or dimension allowing flexibility and variety in use. It contain 3 domains as ;
1. DNA binding domain – This domain binds to responsive elements present in target DNA. It is conserved region of structure.
2. Trans-activation domain – This domain contain binding site for another proteins ( repressor , activator) . This domains do not generate identifiable electron density in the crystallography analysis , which indicates that thay do not form discreate structures and acts as induced fit model
3. Signal sensing domain - Sense external signals and transmits these to rest of transcription complex