| These diagrams represent cross-sections of the bud neck during the final stages of cytokinesis. A ring of septins (gold) lies beneath the cell membrane, while unknown proteins (black arrows) link the actin–myosin ring (blue) to the membrane. Delivery of membrane vesicles (not shown) results in the appearance of Chs2 (red), a transmembrane chitin synthase, in the cell membrane adjacent to the contractile ring. As the actin–myosin ring begins to contract, Chs2 constructs a primary septum (green) behind the inwardly moving membranes, which eventually fuse to generate two separate cells with a primary septum between them. Other chitin synthases then construct a thick secondary septum. Separation of mother and daughter occurs when chitinases digest the primary septum (not shown). Interestingly, Chs2 and the actin–myosin ring are not absolutely essential for cytokinesis in budding yeast; in their absence, an abnormal but effective septum is constructed by the chitin synthases that normally synthesize the secondary septum. Adapted from Cabib, E.: Arch. Biochem. Biophys. 2004, 426:201–207. |
