The receptor-mediated retention of resident proteins in the endoplasmic reticulum

Conclusion Overwhelming evidence has accumulated to support the bulk flow hypothesis which states that proteins entering the exocytic pathway will follow a default route to the plasma membrane unless they carry specific signals for receptor mediated diversion. The resident soluble and membrane proteins of the ER present a clear example of this signal mediated exception to bulk flow. Their study also provides insights relevant to retention or targetting signals operating later in the secretory pathway.The last few years have seen enormous progress in this field, in the delineation of the retention problem, the identification of the retention signal and recently in the identification of components of the retention machinery itself. The next few years hold the promise of a more complete understanding of the retention machinery and of the enigmatic cellular compartment in which it functions.