Early adaptors

Today it is usually harder than in the early days of computer control for operators to interfere with the software, override interlocks, or type in coiTect readings. However, many operators acquire keys or passw ords that they should not have, in much the same way as operators have always unofficially acquired and secreted an assortment of tools and adaptors. On one plant an interlock was found to be illegally blocked the password had been disclosed to 40 people, all of whom denied responsi-aility (see Section 14.5 d). 

Figure 8 Ubiquitin and endocytosis. Receptors on the plasma membrane undergo monoubiquitination as a result of ligand (e.g., neurotransmitter). Ubiquitinated receptors bind to proteins called epsins, which in turn interact with adaptor proteins (adaptin) bound to clathrin-coated pits. Ubiquitination also functions to sort the internalized membrane protein into early endosomes, which directs them to degradation by lysosome through the multivesicular body. If ubiquitin from the endocytosed receptors is removed by an UBP, the receptor recycles back to the membrane. Proteasome inhibitors block endocytotic degradation of some proteins such as glutamate receptor subunits indicating a possible role for the proteasome.

Importantly, non-vesicular transport of GlcCer from its site of synthesis (early Golgi) to distal Golgi compartments is carried out by FAPP2, four-phosphate adaptor protein, controlling the synthesis of glycosphingolipids,... 

In the Chinese hamster ovary cell line ts20, containing a thermosensitive ubiquitin-activating enzyme, El, Sachse et al. (2002) showed that this coat is predominantly present on early endosomes and has a characteristic bilayered appearance in the electron microscope. The coat contains clathrin heavy as well as light chain, but lacks the adaptor complexes API, AP2, and AP3, by which it differs from clathrin coats on endocytic vesicles and recycling endosomes. The coat is insensitive to short incubations with brefeldin A, but disappears in the presence of the phosphatidylinositol 3-kinase inhibitor wortmannin. 

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