RNAse A has these at positions (*) 12 and 119, and two of these and two cysteines are coordinated in most zinc finger motifs.
This substance is modified to form diphthamide, which is found in eukaryotic elongation factor 2 and is ADP-ribosylated by the diphtheria toxin. Addition of guanine is required prior to addition of this compound to its tRNA.  RNAse A has these at positions (*) 12 and 119, and two of these and two cysteines are coordinated in most zinc finger motifs. They are commonly found with serine and aspartate in catalytic triads, and bacteria that are unable to synthesize this amino acid are used in the Ames test. For 10 points, name this amino acid whose side chain includes an imidazole group and which is decarboxylated to make histamine.
This substance is modified to form diphthamide, which is found in eukaryotic elongation factor 2 and is ADP-ribosylated by the diphtheria toxin.
{histidine} [accept {His} or {H}]