This family contains the NMT1 and THI5 proteins. These proteins are proposed to be required for the biosynthesis of the pyrimidine moiety of thiamine [1][2][3]. They are regulated by thiamine [2]. The protein adopts a fold related to the periplasmic binding protein (PBP) family. Both pyridoxal-5'-phosphate (PLP) and an iron atom are bound to the protein suggesting numerous residues of the active site necessary for HMP-P biosynthesis. The yeast protein is a dimer and, although exceptionally using PLP as a substrate, has notable similarities with enzymes dependent on this molecule as a cofactor [4].

1: Functional analysis of yeast gene families involved in metabolism of vitamins B1 and B6. Rodriguez-Navarro S, Llorente B, Rodriguez-Manzaneque MT, Ramne A, Uber G, Marchesan D, Dujon B, Herrero E, Sunnerhagen P, Perez-Ortin JE; Yeast. 2002;19:1261-1276. PMID:12271461

2: nmt1 of fission yeast. A highly transcribed gene completely repressed by thiamine. Maundrell K; J Biol Chem. 1990;265:10857-10864. PMID:2358444

3: The THI5 gene family of Saccharomyces cerevisiae: distribution of homologues among the hemiascomycetes and functional redundancy in the aerobic biosynthesis of thiamin from pyridoxine. Wightman R, Meacock PA; Microbiology. 2003;149:1447-1460. PMID:12777485

4: The last piece in the vitamin B1 biosynthesis puzzle: structural and functional insight into yeast 4-amino-5-hydroxymethyl-2-methylpyrimidine phosphate (HMP-P) synthase. Coquille S, Roux C, Fitzpatrick TB, Thore S; J Biol Chem. 2012;287:42333-42343. PMID:23048037