************************************
* Intermediate filaments signature *
************************************

Intermediate filaments (IF) [1,2] are proteins which are primordial components
of the cytoskeleton and the nuclear envelope.  They generally form filamentous
structures 8 to 14 nm wide.  IF proteins are members of a very large multigene
family of proteins which has been subdivided in seven subgroups:

 - Type   I: Acidic cytokeratins.
 - Type  II: Basic cytokeratins.
 - Type III: Vimentin,  desmin,   glial  fibrillary  acidic  protein   (GFAP),
   periferin, and plasticin.
 - Type  IV: Neurofilaments L, H and M, and alpha-internexin [3].
 - Type   V: Nuclear lamins A, B, and C [4].
 - Type  VI: Nestin [5].
 - Invertebrate (snails and nematodes) non-neuronal cytoplasmic IF [6].

All IF proteins  are structurally  similar in  that they consist of: a central
rod domain comprising  some 300 to  350 residues which is  arranged in coiled-
coiled alpha-helices,  with at least two short characteristic interruptions; a
N-terminal non-helical  domain  (head)  of variable  length; and a  C-terminal
domain (tail)  which is also   non-helical,  and which   shows  extreme length
variation between different IF proteins.

While IF proteins are evolutionary and structurally related, they have limited
sequence homologies  except in several regions of the rod domain. We use, as a
sequence pattern  for  this  class of  proteins,  a conserved  region  at  the
C-terminal extremity of the rod domain.

-Consensus pattern: [IV]-x-[TACI]-Y-[RKH]-x-[LM]-L-[DE]
-Sequences known to belong to this class detected by the pattern: ALL,  except
 for Drosophila lamin DM0.
-Other sequence(s) detected in SWISS-PROT: rabbit lactase-phlorizin  hydrolase
 and Streptomyces hygroscopicus acetyl-hydrolase.

-Note: in the third position of  the pattern, Ala is found in type IV and V IF
 proteins, Thr is found in IF proteins of  type I, II, III, and VI,  Cys in IF
 from snails, and Ile in IF from worms.   In the first position of the pattern
 Val is found in type VI, Ile is found in all other types.

-Last update: June 1994 / Pattern and text revised.

[ 1] Steiner P.M., Roop D.R.
     Annu. Rev. Biochem. 57:593-625(1988).
[ 2] Stewart M.
     Curr. Opin. Cell Biol. 2:91-100(1990).
[ 3] Fliegner K.H., Ching G.Y., Liem R.K.H.
     EMBO J. 9:749-755(1990).
[ 4] Franke W.W.
     Cell 48:3-4(1987).
[ 5] Lendahl U., Zimmerman L.B., McKay R.D.G.
     Cell 60:585-595(1990).
[ 6] Dodemont H., Riemer D., Weber K.
     EMBO J. 9:4083-4094(1990).