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How does the Golgi complex regulate the insertion of plasma membrane proteins?
Can proteins be transported back to the rough endoplasmic reticulum?
Sometimes vital proteins needed in the rough endoplasmic reticulum are transported along with the other proteins in the Golgi complex. The Golgi complex has a mechanism for trapping them and sending them back to the rough endoplasmic reticulum.
This cartoon shows the process. The protein destined for secretion is red. The blue protein must remain in the rough endoplasmic reticulum. The rough endoplasmic reticulum has inserted a receptor protein on the membrane it sends to the Golgi complex in the transitional vesicles (shown in green). These are retrograde vesicles and are therefore coated with "COPI" (coatamer). The ER protein receptor captures all of the protein that carries the ER residency signal. . Vesicles then bud from the Golgi complex and move back to the rough endoplasmic reticulum. The receptor can circulate and continue to return the proteins needed by the endoplasmic reticulum.
A drug called "brefeldin A" blocks the transfer of protein to the Golgi complex, however the reverse transport is not blocked. The following electron micrograph shows the results of an experiment after a brefeldin A block.
For more information, see also, Cole, N.B., Ellenberg, J, Song, J, DiEuliis, D and Lippincott-Schwartz, J. Retrograde transport of Golgi-localized proteins to the ER. J Cell Biol 1-15, 1998.