 Human p14ARF, however, does not contain any lysines, and mouse p19Arf only contains one lysine.If the mouse lysine is replaced with arginine, there is no effect on its degradation, suggesting it is also ubiquinated at the N-terminus.This adds to the uniqueness of the ARF proteins, because most eukaryotic proteins are acetylated at the N-terminus, preventing ubiquination at this location.