 In AP-1 it is named γ (gamma), AP-2 has α (alpha), AP-3 has δ (delta), AP-4 has ε (epsilon) and AP-5 has ζ (zeta).The two smaller proteins are a medium subunit named μ (mu ∼50 kD) and a small subunit σ (sigma ∼20 kD), and named 1 through 5 corresponding to the 5 AP complexes.Components of COPI (cop one) a coatomer, and TSET (T-set) a membrane trafficking complex have similar heterotetramers of the AP complexes.