InterPro domain: IPR001937

Galactose-1-phosphate uridyl transferase 2.7.7.12 (GalT) catalyses 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.

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 E. coli or Streptomyces lividans, while class-II enzymes have been found so far only in bacteria such as Bacillus subtilis or Lactobacillus helveticus [ 2 ].

1. 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, 9017-26
2. Galactose utilization in Lactobacillus helveticus: isolation and characterization of the galactokinase (galK) and galactose-1-phosphate uridyl transferase (galT) genes. J. Bacteriol. 173, 4464-73