Oligomerization of a membrane protein correlates with its retention in the Golgi complex

ization did not occur under several conditions that block ER to Golgi transport. The lumenal domain was not required for oligomerization since another chimera (otmlG), where the lumenal domain of Gml was replaced by the o~ subunit of human chorionic gonadotropin, also formed an SDS-resistant oligomer, and was able to form hetero-oligomers with Gml as revealed by coprecipitation experiments. SDS resistance was conferred by the cytoplasmic tail of VSV G, because proteolytic digestion of the tail in microsomes containing Gml oligomers resulted in loss of SDS resistance, although the protease-treated material continued to migrate as a large oligomer on sucrose gradients. Interestingly, treatment of cells with cytochalasin D blocked formation of SDS-resistant (but not SDS-sensitive) oligomers. Our data suggest that SDS-resistant oligomers form as newly synthesized molecules of Gml arrive at the Golgi complex and may interact (directly or indirectly) with an actinbased cytoskeletal matrix. The oligomerization of Gml and other resident proteins could serve as a mechanism for their retention in the Golgi complex.