{PDOC50097}
{PS50097; BTB}
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* BTB domain profile *
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The BTB domain (Broad-Complex, Tramtrack and Bric a brac) is also known as the
POZ domain  (POxvirus  and  Zinc  finger).  It  is  a  homodimerization domain
occurring at  the  N-terminus of proteins containing multiple copies of either
zinc fingers    of    the  C2H2 type (see <PDOC00028>) or Kelch repeats [1,2].
Many BTB  proteins  are  transcriptional  regulators  that  are thought to act
through the control of chromatin structure.

The structure  of  the  BTB  domain  of the promyelocytic leukemia zinc finger
(PLZF) protein  has  been  determined  by  X-ray crystallography and reveals a
tightly intertwined  dimer  with  an  extensive  hydrophobic  interface [3]. A
surface-exposed groove lined with conserved amino acids is formed at the dimer
interface, suggesting a peptide-binding site.

Some proteins known to contain a BTB/TTK domain are listed below:

 - Mammalian Bach proteins. These transcriptional regulators act as repressors
   or activators.
 - Mammalian B-cell lymphoma 6 protein (BCL-6). A transcriptional regulator.
 - Mammalian   calicin.   A   possible  morphogenic  cytoskeletal  element  in
   spermiogenic differenciation.
 - Human  promyelocytic  leukemia zinc finger (PLZF). A probable transcription
   factor.
 - Drosophila GAGA transcription factor.
 - Drosophila  Mod(MDG4)  or E(VAR)3-93D. A chromatin protein involved in gene
   silencing in  position  effect  variegation, the control of gypsy insulator
   sequence, maintenance of gene expression, and apoptosis.
 - Drosophila Tramtrack (TTK) protein. A probable transcriptional repressor.
 - Drosophila  Kelch  protein.  A  component of ring canals that regulates the
   flow of cytoplasm between cells.
 - Vaccinia virus proteins A55, C2, C4, C13, and F3.
 - Myxoma virus proteins M-T8 and M-T9.

-Sequences known to belong to this class detected by the profile: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.
-Last update: December 2001 / First entry.

[ 1] Zollman S., Godt D., Prive G.G., Couderc J.L., Laski F.A.
     "The BTB domain, found primarily in zinc finger proteins, defines an
     evolutionarily conserved family that includes several developmentally
     regulated genes in Drosophila."
     Proc. Natl. Acad. Sci. U.S.A. 91:10717-10721(1994).
     PubMed=7938017
[ 2] Bardwell V.J., Treisman R.
     "The POZ domain: a conserved protein-protein interaction motif."
     Genes Dev. 8:1664-1677(1994).
     PubMed=7958847
[ 3] Ahmad K.F., Engel C.K., Prive G.G.
     "Crystal structure of the BTB domain from PLZF."
     Proc. Natl. Acad. Sci. U.S.A. 95:12123-12128(1998).
     PubMed=9770450

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