The membrane transport factor p115 recycles only between homologous compartments in intact heterokaryons

GARCIA MATA, R; GAO, Y; ALVAREZ, C; SZTUL, E

EUROPEAN JOURNAL OF CELL BIOLOGY

ELSEVIER GMBH

Año: 2000 vol. 79 p. 229 - 239

0171-9335

Cytosolic proteins that participate in membrane traffic areassumed to be recruited from the cytosol onto specificmembrane sites where they perform their function, and thenreleased into cytosol before rebinding to catalyze anotherround of transport. To examine whether the ER to Golgitransport factor p115 recycles through release into a cytosolicpool, we formed heterokaryons between rat NRK and simianCOS-7 cells and examined the dynamics of rat p115 transferfrom the rat to the simian portion of the heterokaryon. Theheterokaryons shared a common cytosolic pool, as shown bythe efficient relocation of a cytosolic green fluorescent protein(GFP) from the COS-7 to the NRK part of the heterokaryon.Unexpectedly, even 24 h after cell fusion, rat p115 did notredistribute to the COS-7 part of the heterokaryon. This wasnot due to the inability of the rat p115 to associate with simianmembranes since rat p115 expressed in COS-7 cells wasefficiently targeted to and associated with simian Golgicomplex. Furthermore, rat p115 associated with heterologoussimian membranes after the NRK and COS-7 Golgi fused intoa single chimeric structure. Our results indicate that p115 is notfreely diffusible in intact cells and might remain tethered tomembranes throughout its life cycle. These findings suggestthat p115, and perhaps other cytosolic proteins involved inmembrane traffic, recycle not by being released into cytosol,but in association with recycling membranes