****************************************
* Bipartite nuclear targeting sequence *
****************************************

The uptake  of protein by  the   nucleus  is extremely selective   and nuclear
proteins must therefore  contain within  their final  structure a signal  that
specifies selective accumulation in the nucleus [1,2]. Studies on some nuclear
proteins, such as  the  large T antigen of SV40,  have indicated which part of
the sequence  is  required  for  nuclear  translocation.   The  known  nuclear
targeting sequences  are   generally  basic, but  there  seems to  be no clear
common denominator  between  all the known sequences.  Although some consensus
sequence patterns have  been proposed (see for example [3]),  the current best
strategy to detect a nuclear targeting sequence is based [4] on  the following
definition of what is called a 'bipartite nuclear targeting sequence':

  (1) Two adjacent basic amino acids (Arg or Lys).
  (2) A spacer region of any 10 residues.
  (3) At least three basic residues (Arg or Lys) in the five positions
      after the spacer region.

-Sequences known to belong to this class detected by the pattern: 56% of known
 nuclear proteins according to [4].
-Other sequence(s) detected in SWISS-PROT: about 4.2% of  non-nuclear proteins
 according to [4].

-Last update: October 1993 / Text revised.

[ 1] Dingwall C., Laskey R.A.
     Annu. Rev. Cell Biol. 2:367-390(1986).
[ 2] Garcia-Bustos J., Heitman J., Hall M.N.
     Biochim. Biophys. Acta 1071:83-101(1991).
[ 3] Gomez-Marquez J., Segade F.
     FEBS Lett. 226:217-219(1988).
[ 4] Dingwall C., Laskey R.A.
     Trends Biochem. Sci. 16:478-481(1991).