This family represents the N terminal region of the enzyme arginine-tRNA-protein transferase (EC 22.214.171.124), which catalyzes the post-translational conjugation of arginine to the N-terminus of a protein. In eukaryotes, this functions as part of the N-end rule pathway of protein degradation by conjugating a de-stabilizing amino acid to the amino terminal aspartate or glutamate of a protein, targeting the protein for ubiquitin-dependent proteolysis. N terminal cysteine is sometimes modified. In S cerevisiae, Cys20, 23, 94 and/or 95 are thought to be important for activity. Of these, only Cys 94 appears to be completely conserved in this family.