G. Griffiths et al., IMMUNOCYTOCHEMICAL LOCALIZATION OF BETA-COP TO THE ER-GOLGI BOUNDARY AND THE TGN, Journal of Cell Science, 108, 1995, pp. 2839-2856
Recent data strongly suggest that the coatomer (COP) complex is involv
ed in membrane transport between the ER and Golgi complex. This vesicu
lar coat has been implicated in ER to Golgi, in intra Golgi as well as
in Golgi to ER traffic. In this study we present a detailed immunocyt
ochemical analysis of the distribution of beta-COP in different tissue
culture cells. Our results extend previous studies by showing, using
electron microscopy, that beta-COP accumulates on vesicular profiles a
nd buds in the intermediate compartment (IC) under conditions that blo
ck ER to Golgi transport (15 degrees C), Importantly, under these cond
itions beta-COP co-localizes on these structures with a passenger prot
ein, the membrane glycoprotein of vesicular stomatis virus (ts-O45-G).
Furthermore, quantitative immunofluorescence microscopy of cells with
ts-045-G accumulated in the ER, IC and trans-Golgi network, shifted b
riefly to the permissive temperature, showed that beta-COP was associa
ted with many of the putative transport intermediates containing the v
iral glycoprotein which is in transit between the ER/IC and the cis-Go
lgi. The simplest interpretation of these data is that COP-coated vesi
cles are involved in anterograde transport of ts-045-G from the IC to
the Golgi complex. Since many putative COP vesicles lacked the G prote
in following release of the 15 degrees C block this pool could be invo
lved in retrograde transport. We also show that beta-COP is present on
the membranes of the trans-Golgi network. However, in contrast to the
ER-Golgi boundary, we could find no convincing evidence that this poo
l of beta-COP is associated with buds or trans-Golgi network-derived t
ransport vesicles.