It has a special sequence of three amino acids: serine-tyrosine-glycine (sometimes, the serine is replaced by the similar threonine).

• 这个机制只由3个氨基酸组成，并且有着特定的顺序：丝氨酸-酪氨酸-氨基乙酸（有时丝氨酸会被苏氨酸所取代）。