The function of DPH1 (diphthamide biosynthesis 1, Ensembl gene identifier ENSG00000108963) is as follows. Catalyzes the first step of diphthamide biosynthesis, a post- translational modification of histidine which occurs in elongation factor 2 (PubMed:30877278). DPH1 and DPH2 transfer a 3-amino-3- carboxypropyl (ACP) group from S-adenosyl-L-methionine (SAM) to a histidine residue, the reaction is assisted by a reduction system comprising DPH3 and a NADH-dependent reductase (By similarity). Acts as a tumor suppressor (PubMed:10519411). {ECO:0000250|UniProtKB:P40487, ECO:0000269|PubMed:10519411, ECO:0000269|PubMed:30877278}.