The schematic diagram of N-end rule in bacteria. (A) Relatively long protein half-life. If the second N-terminal amino-acid is A, G, S, C or P and in some cases V or T, which can be processed by methionine aminopeptidase (MetAP), the protein will have a long half-life. (B) Relatively short protein half-life. When the second N-terminal amino-acid is W, Y, F, L, R, K, M, D, E, I, H, Q or N, which can not be processed by MetAP, the protein will have a short half-life.