title: B3 domain
text: # B3 domain
  
  The B3 DNA binding domain (DBD) is a highly conserved domain found exclusively in transcription factors (≥40 species) (Pfam PF02362) combined with other domains (InterPro: IPR003340). It consists of 100-120 residues, includes seven beta strands and two alpha helices that form a DNA-binding pseudobarrel protein fold (SCOP 117343); it interacts with the major groove of DNA.
  
  ## B3 families
  
  In Arabidopsis thaliana, there are three main families of transcription factors that contain B3 domain:
  
  * ARF (Auxin Response Factors)
  * ABI3 (ABscisic acid Insensitive3)
  * RAV (Related to ABI3/VP1)
  
  | protein | ARF1-B3 | ABI3-B3 | RAV1-B3 |
  | - | - | - | - |
  | B3 structure derived by | molecular model | molecular model | NMR |
  | B3 recognition sequence | TGTCTC | CATGCA | CACCTG |
  
  PDB: 1WID​ and PDB: 1YEL​ are only known NMR solution phase structures of the B3 DNA Binding Domain.
  
  ## Related proteins
  
  The N-terminal domain of restriction endonuclease EcoRII; the C-terminal domain of restriction endonuclease BfiI possess a similar DNA-binding pseudobarrel protein fold.
  
  