{PDOC00108}
{PS00117; GAL_P_UDP_TRANSF_I}
{PS01163; GAL_P_UDP_TRANSF_II}
{BEGIN}
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* Galactose-1-phosphate uridyl transferase signatures *
*******************************************************

Galactose-1-phosphate  uridyl  transferase (EC 2.7.7.12) (galT)  catalyzes the
transfer of an uridyldiphosphate group on  galactose (or glucose) 1-phosphate.
During the  reaction,  the  uridyl moiety links to a histidine residue. In the
Escherichia coli  enzyme,  it  has  been shown [1] that two histidine residues
separated by   a single proline residue are essential for enzyme activity. The
first one is a ligand to a zinc ion and the second act as a nucleophile.

On the  basis of sequence similarities, two apparently unrelated families seem
to exist.  Class-I  enzymes  are  found in eukaryotes as well as some bacteria
such as Escherichia coli or Streptomyces lividans, while class-II enzymes have
been found  so  far  only  in  some  Gram-positive  bacteria  such as Bacillus
subtilis or Lactobacillus helveticus [2].

We developed  signature  patterns for both  families.  For class-I enzymes the
signature is  based on the active site residues. For class-II enzymes we chose
a region which also includes two conserved histidines.

-Consensus pattern: F-E-N-[RK]-G-x(3)-G-x(4)-H-P-H-x-Q
                    [The first H binds zinc and the second H is an active site
                    residue]
-Sequences known to belong to this class detected by the pattern: ALL  class-I
 enzymes.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Consensus pattern: D-L-P-I-[VS]-G-G-[ST]-[LIVM](2)-[STAV]-H-[DEN]-H-[FY]-Q-
                    [GAT]-G
-Sequences known to belong to this class detected by the pattern: ALL class-II
 enzymes.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Note: Class-I  enzymes are structurally related to the HIT family of proteins
 (see <PDOC00694>).

-Last update: December 2004 / Pattern and text revised.

[ 1] Reichardt J.K.V., Berg P.
     "Conservation of short patches of amino acid sequence amongst proteins
     with a common function but evolutionarily distinct origins:
     implications for cloning genes and for structure-function analysis."
     Nucleic Acids Res. 16:9017-9026(1988).
     PubMed=2845364
[ 2] Mollet B., Pilloud N.
     "Galactose utilization in Lactobacillus helveticus: isolation and
     characterization of the galactokinase (galK) and galactose-1-phosphate
     uridyl transferase (galT) genes."
     J. Bacteriol. 173:4464-4473(1991).
     PubMed=2066342

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