Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 92

Many processes ensure that the chromosomes are physically separate, yet are gathered together in a manageable way in the bacterial cell. With circular chromosomes, an uneven number of recombination events will regularly form dimer chromosomes, where the two circles join to form one large circle that cannot be subdivided into daughter cells. The highly controlled process of dimer resolution with XerC, XerD, and FtsK in E. coli ensures that dimer chromosomes are kept separate without accidently making dimers out of separate chromosomes before they can be passed to the daughter cells. Circular chromosomes can also become conjoined like the rings on a chain that cannot be passed on to daughter cells. Another highly regulated process by Topo IV removes these links between the chromosomes. Regulation of Topo IV activity with condensation and FtsK transport, as shown in Figure 1.19, plays an important role in making sure the enzyme separates interlinked chromosomes and does not link them together. A number of processes compact the chromosomes in bacteria. Condensins gather regions of the chromosome together that are, in turn, held together by a number of nonspecific DNA-binding proteins to allow compaction of the bacterial chromosome. This process is facilitated by supercoiling that allows the chromosome to twist around itself. In the next section, we learn how chromosomes are efficiently partitioned into each daughter cell during the process of cell division.