p24 and p23, the major transmembrane proteins of COPI-coated transport vesicles, form hetero-oligomeric complexes and cycle between the organelles ofthe early secretory pathway

COPI-coated vesicles that bud off the Golgi complex contain two major trans membrane proteins, p23 and p24, We have localized the protein at the Golgi complex: and at COPI-coated vesicles. Transport from the intermediate compa rtment (IC) to the Golgi can be blocked at 15 degrees C, and under these co nditions p24 accumulates in peripheral punctated structures identified as I C, Release from the temperature block leads to a redistribution of p24 to t he Golgi, showing that p24, similar to p23, cycles between the IC and Golgi complex. Immunoprecipitations of p24 from cell lysates and from detergent- solubilized Golgi membranes and COPI-coated vesicles show that p24 and p23 interact with each other to form a complex. Transient transfection of p23 i n HeLa cells shows that p23 and p24 colocalize in structures induced by the overexpression of p23, Taken together p24 interacts with p23 and constitut ively cycles between the organelles of the early secretory pathway. (C) 199 9 Federation of European Biochemical Societies.