Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 96

Much has also been learned about how the bacterial division septum forms. This process is called cytokinesis. A protein called FtsZ, which forms a ring around the midpoint of the cell, performs the primary step in this process (Figure 1.21b). This protein is related to tubulin of eukaryotes and forms filaments that grow and shorten by adding and removing shorter filaments, called protofilaments, to its ends in the presence of GTP. Before the cell is ready to divide, the FtsZ protein exists as helical filaments that traverse the cell. When the cell is about to divide, these filaments converge on the middle of the cell and form a ring at the site of the future septum. The FtsZ ring then attracts many other proteins, including the DNA translocase FtsK discussed above. FtsZ helps form the division septum, which eventually squeezes the mother cell at its center to allow the formation of the two daughter cells. The following major questions may be asked: why does the septum form only in the middle of the cell, and why does septum formation not occur over the nucleoid prior to chromosome segregation? The answers to these questions lie, at least in part, in two types of systems: the Min systems and the nucleoid occlusion systems.