A specialized cellular substructure has been identified in which such decisions may be made, but on what basis is still unclear. One can envisage Ginsenoside-F4 termination of the exchange reaction based on generation of a true DM-mediated “compact” conformation. The answer may lie in elucidating the molecular details of the resolution of the tetramolecular complex. The “compare-exchange” mechanism proposed here for DM mechanism might also be important for antigen processing via the MHC class I pathway. MHC class I processing involves proteins structurally related to MHCII, and both classes of MHC molecules undergo peptide-dependent conformational change. Furthermore, the majority of MHC class I alleles requires the intervention of the tapasin-ERp57 heterodimer to optimize their peptide cargo. The “compare-exchange” mechanism may provide additional insights into the biology of MHC antigen processing, and may also be generally applicable to other biological systems in which protein receptors must bind diverse yet structurally related ligands. An increasing number of reports have highlighted the function of the primary cilium in the control of several physiological processes. The PC is a hair-like cellular extension found at the surface of most vertebrate cells. This sophisticated microtubulebased organelle has been shown to sense multiple mechanical and chemical stimuli from the environment and to elicit specific cellular responses, which play crucial roles in embryonic development and homeostatic processes in adulthood. The PC has also recently been implicated in the regulation of cell cycle progression and, as a consequence, a lack of PC was associated with increased proliferation. PC formation takes place in quiescent or differentiated cells. PCs are assembled from the mother centriole of the unique centrosome present in these cells, which therefore corresponds to the basal body of PC. which forms the skeleton of this “antenna” like extension of the plasma membrane. Whereas the basal body shares many properties with classical centrosomes, made of two Catharanthine sulfate centrioles and of a pericentriolar matrix, the axoneme represents a unique domain, characterized by the exclusion of many proteins and the enrichment of specific soluble, cytoplasmic, as well as membrane-associated components.