Adaptor Related Protein Complex 4 Sigma 1 (AP4s1)

The heterotetrameric adaptor protein (AP) complexes sort integral membrane proteins at various stages of the endocytic and secretory pathways. The predicted 144-amino acid Ap4s1 protein has a calculated molecular mass of 16.8 kD. Northern blot analysis revealed a 1.2- to 1.4-kb transcript in all mouse tissues examined.

AP4S1 shows an apparent molecular mass of about 17 kD and is part of a 280-kD complex containing AP4B1, AP4E1, and AP4M1. Immunolocalization of the AP4B1 subunit in HeLa cells indicated that the AP4 complex associates with the trans-Golgi network or an adjacent structure. The association was sensitive to brefeldin-A treatment, indicating that the membrane localization of AP4 is dependent upon the small GTP-binding protein ARF1.