InterPro domain: IPR014640

Members of this group are eukaryotic bifunctional enzymes with glutamine amidotransferase ( IPR017926 ) and cyclase activities ( IPR006062 ) that catalyse the fifth and sixth steps of the histidine biosynthetic pathway. In eubacteria, these steps are catalysed by a complex formed by two subunits, namely the glutamine amidotransferase HisH ( PIRSF000495 ) and the cyclase HisF ( PIRSF001454 ) which are encoded in the same operon [ 1 ].

The catalytic activity has been assessed for many members, mainly by complementation assays. The Saccharomyces cerevisiae (Baker s yeast) member is able to suppress His auxotrophy of corresponding Escherichia coli hisH and hisF mutants [ 2 ]. In plants, hisHF cDNA from Emericella nidulans (Aspergillus nidulans) and Arabidopsis thaliana (Mouse-ear cress) complemented a S. cerevisiae his7Delta strain [ 3 , 4 ]. In addition, A. nidulans cDNA complemented E. coli hisH and hisF mutant strains [ 5 ].

1. Histidine biosynthetic pathway and genes: structure, regulation, and evolution. Microbiol. Rev. 60, 44-69
2. Cloning, primary structure, and regulation of the HIS7 gene encoding a bifunctional glutamine amidotransferase: cyclase from Saccharomyces cerevisiae. J. Bacteriol. 175, 5548-58
3. An Arabidopsis cDNA encoding a bifunctional glutamine amidotransferase/cyclase suppresses the histidine auxotrophy of a Saccharomyces cerevisiae his7 mutant. FEBS Lett. 428, 229-34
4. Regulation of hisHF transcription of Aspergillus nidulans by adenine and amino acid limitation. Fungal Genet. Biol. 32, 21-31