Figure 1. Crosstalk between the Arg/N-end rule pathway and the Ac/N-end rule pathway. Nearly all nascent proteins bear N-terminal Met due to the AUG start codon. The Arg/N-end rule pathway targets for degradation proteins with unacetylated N-terminal Met if it is followed by a large hydrophobic Ф residue (Leu, Ile, Phe, Tyr, Trp) at position 2. Nt-acetylase catalyzes Nt-acetylation of the Met-Ф proteins either cotranslationally or posttranslationally, and thereby creates the Ac/Met-Ф degrons for the Ac/N-end rule pathway.