|PROSITE documentation PDOC00108 [for PROSITE entry PS00117]|
Galactose-1-phosphate uridyl transferase (EC 22.214.171.124) (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  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 .
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.Note:
Class-I enzymes are structurally related to the HIT family of proteins (see <PDOC00694>).Last update:
December 2004 / Pattern and text revised.
PROSITE methods (with tools and information) covered by this documentation:
|1||Authors||Reichardt J.K.V. Berg P.|
|Title||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.|
|Source||Nucleic Acids Res. 16:9017-9026(1988).|
|2||Authors||Mollet B. Pilloud N.|
|Title||Galactose utilization in Lactobacillus helveticus: isolation and characterization of the galactokinase (galK) and galactose-1-phosphate uridyl transferase (galT) genes.|
|Source||J. Bacteriol. 173:4464-4473(1991).|