PROSITE documentation PDOC00108
Galactose-1-phosphate uridyl transferase signatures


Galactose-1-phosphate uridyl transferase (EC (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.


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

Last update:

December 2004 / Pattern and text revised.


Technical section

PROSITE methods (with tools and information) covered by this documentation:

GAL_P_UDP_TRANSF_I, PS00117; Galactose-1-phosphate uridyl transferase family 1 active site signature  (PATTERN)

GAL_P_UDP_TRANSF_II, PS01163; Galactose-1-phosphate uridyl transferase family 2 signature  (PATTERN)


1AuthorsReichardt J.K.V. Berg P.
TitleConservation 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.
SourceNucleic Acids Res. 16:9017-9026(1988).
PubMed ID2845364

2AuthorsMollet B. Pilloud N.
TitleGalactose utilization in Lactobacillus helveticus: isolation and characterization of the galactokinase (galK) and galactose-1-phosphate uridyl transferase (galT) genes.
SourceJ. Bacteriol. 173:4464-4473(1991).
PubMed ID2066342

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