GO:0017183:   peptidyl-diphthamide biosynthetic process from peptidyl-histidine
The modification of peptidyl-histidine to 2"-(3-carboxamido-3-(trimethylammonio)propyl)-L-histidine, known as diphthamide, found in translation elongation factor EF-2. The process occurs in eukaryotes and archaea but not eubacteria.