This domain family is found in bacteria and eukaryotes, and is approximately 190 amino acids in length. This family is the N terminal of GTP cyclohydrolase, the rate limiting enzyme in the synthesis of tetrahydrobiopterin.

1: Identification and Functional Characterization of Phosphorylation Sites on GTP Cyclohydrolase I. Du J, Wei N, Xu H, Ge Y, Vasquez-Vivar J, Guan T, Oldham KT, Pritchard KA Jr, Shi Y; Arterioscler Thromb Vasc Biol. 2009; [Epub ahead of print] PMID:19762783