In most cases, the transcription factors in eukaryotes which bind to promoter   or enhancer sequences   are activator   proteins   which induce   transcription.   That proteins generally have at least two distinct domains of protein structure, a DNA- binding  domain  which identify  the specific DNA sequence  to bind to and an activation  domain responsible  for bringing  about the transcriptional  activation by  interaction  with  other  transcription   factors  and the  RNA  polymerase molecule. Various transcription factors operate as dimers, either homodimers (identical subunits) or heterodimers (dissimilar subunits) with the subunits held together through dimerization domains. The DNA dimerization domains and binding domains have characteristic protein structures (motifs) which are explained

Figure: Looping out of DNA permitting the interaction of enhancer-bound factor(s) with the transcription initiation complex.

below. At last, some transcription factors example for steroid hormone receptors are responsive  to specific  short  molecules  (ligands)  that  regulate  the activity  of the  transcription  factor.  In these cases, the ligand binds at a ligand-binding domain.