****************************************************************
* Fibrinogen beta and gamma chains C-terminal domain signature *
****************************************************************

Fibrinogen [1], the  principal protein of  vertebrate  blood  clotting  is  an
hexamer containing two  sets  of  three  different  chains  (alpha,  beta, and
gamma), linked to  each  other by  disulfide bonds. The N-terminal sections of
these three chains are  evolutionary  related  and  contain the cysteines that
participate in   the  cross-linking  of  the  chains.  However,  there  is  no
similarity between the C-terminal part of the alpha chain and that of the beta
and gamma chains.  The C-terminal  part of the beta and gamma  chains  forms a
domain of   about   270   amino-acid  residues.  As  shown  in  the  schematic
representation this domain contains four  conserved  cysteines involved in two
disulfide bonds.

                                                           *****
  xxxxxxCxxxxxxxxxxxxCxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxCxxxxxCxxxxxxxxxxxxx
        |            |                                 |     |
        +------------+                                 +-----+

'C': conserved cysteine involved in a disulfide bond.
'*': position of the pattern.

Such a domain has been recently found [2,3] in other proteins which are listed
below.

 - Two sea cucumber  fibrinogen-like proteins (FReP-A and FReP-B).  These  are
   proteins, of  about  260 amino acids, which have a fibrinogen beta/gamma C-
   terminal domain.
 - In the C-terminus of  Drosophila  protein scabrous (gene sca).  Scabrous is
   involved in the regulation of neurogenesis in Drosophila and may  encode  a
   lateral inhibitor of R8 cells differentiation.
 - In the C-terminus  of  a  mammalian  T-cell  specific  protein  of  unknown
   function.
 - In the C-terminus  of a  human protein of unknown function which is encoded
   on the  opposite  strand of the steroid 21-hydroxylase/complement component
   C4 gene locus.

The function of this domain  is  not  yet known, but it has been suggested [2]
that it could be  involved  in protein-protein interactions.  As  a  signature
pattern for this domain, we selected the region around the fourth cysteine.

-Consensus pattern: W-W-[LIVMFYW]-x(2)-C-x(2)-[SGSA]-x(2)-N-G
                    [C is involved in a disulfide bond]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in SWISS-PROT: NONE.
-Last update: December 1991 / First entry.

[ 1] Doolittle R.F.
     Annu. Rev. Biochem. 53:195-229(1984).
[ 2] Xu X., Doolittle R.F.
     Proc. Natl. Acad. Sci. U.S.A. 87:2097-2101(1990).