Diphthamide_syn, diphthamide synthase, catalyses the last amidation step of diphthamide biosynthesis using ammonium and ATP. Swiss:Q16439 is a candidate tumour suppressor gene [1]. DPH2 from yeast Swiss:P32461 [2], which confers resistance to diphtheria toxin has been found to be involved in diphthamide synthesis. Diphtheria toxin inhibits eukaryotic protein synthesis by ADP-ribosylating diphthamide, a post-translationally modified histidine residue present in EF2. Diphthamide synthase is evolutionarily conserved in eukaryotes. Diphthamide is a post-translationally modified histidine residue found on archaeal and eukaryotic translation elongation factor 2 (eEF-2) [3].

1: A cDNA from the ovarian cancer critical region of deletion on chromosome 17p13.3. Phillips NJ, Zeigler MR, Deaven LL; Cancer Lett 1996;102:85-90. PMID:8603384

2: Diphthamide synthesis in Saccharomyces cerevisiae: structure of the DPH2 gene. Mattheakis LC, Sor F, Collier RJ; Gene 1993;132:149-154. PMID:8406038

3: Chemogenomic approach identified yeast YLR143W as diphthamide synthetase. Su X, Lin Z, Chen W, Jiang H, Zhang S, Lin H; Proc Natl Acad Sci U S A. 2012;109:19983-19987. PMID:23169644