Proteins involved in steps 4 and 6 of the histidine biosynthesis pathway are contained in this family. Histidine is formed by several complex and distinct biochemical reactions catalysed by eight enzymes. The enzymes in this Pfam entry are called His6 and His7 in eukaryotes and HisA and HisF in prokaryotes. The structure of HisA is known to be a TIM barrel fold. In some archaeal HisA proteins the TIM barrel is composed of two tandem repeats of a half barrel e.g. Swiss:P05325 [2]. This family belong to the common phosphate binding site TIM barrel family [3].

1: Paralogous histidine biosynthetic genes: evolutionary analysis of the Saccharomyces cerevisiae HIS6 and HIS7 genes. Fani R, Tamburini E, Mori E, Lazcano A, Lio P, Barberio C, Casalone E, Cavalieri D, Perito B, Polsinelli M, Gene 1997;197:9-17. PMID:9332345

2: The evolution of the histidine biosynthetic genes in prokaryotes: a common ancestor for the hisA and hisF genes. Fani R, Lio P, Chiarelli I, Bazzicalupo M; J Mol Evol 1994;38:489-495. PMID:8028028

3: Homology among (betaalpha)(8) barrels: implications for the evolution of metabolic pathways. Copley RR, Bork P; J Mol Biol 2000;303:627-641. PMID:11054297