TARGETING SIGNALS AND SUBUNIT INTERACTIONS IN COATED VESICLE ADAPTER COMPLEXES

There are two clathrin-coated vesicle adaptor complexes in the cell, o ne associated with the plasma membrane and one associated with the TGN . The subunit composition of the plasma membrane adaptor complex is al pha-adaptin, beta-adaptin, AP50, and AP17; while that of the TGN adapt or complex is gamma-adaptin, beta'-adaptin, AP47, and AP19. To search for adaptor targeting signals, we have constructed chimeras between al pha-adaptin and gamma-adaptin within their NH2-terminal domains. We ha ve identified stretches of sequence in the two proteins between amino acids similar to 130 and 330-350 that are essential for targeting. Imm unoprecipitation reveals that this region determines whether a constru ct coassembles with AP50 and AP17, or with AP47 and AP19. These observ ations suggest that these other subunits may play an important role in targeting. In contrast, beta- and beta'-adaptins are clearly not invo lved in this event. Chimeras between the alpha- and gamma-adaptin COOH -terminal domains reveal the presence of a second targeting signal. We have further investigated the interactions between the adaptor subuni ts using the yeast two-hybrid system. Interactions can be detected bet ween the beta/beta'-adaptins and the alpha/gamma-adaptins, between the beta/beta'-adaptins and the AP50/AP47 subunits, between alpha-adaptin and AP17, and between gamma-adaptin and AP19. These results indicate that the adaptor subunits act in concert to target the complex to the appropriate membrane.