Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico, USA.
Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico, USA
mBio. 2019 Jul 30;10(4):e01002-19. doi: 10.1128/mBio.01002-19.
Maintaining the integrity of the genome is essential to cell survival. In the bacterium , the single circular chromosome exhibits a specific orientation in the cell, with the replication origin () residing at the pole of the cell bearing a stalk. Upon initiation of replication, the duplicated centromere-like region and move rapidly to the opposite pole where is captured by a microdomain hosting a unique set of proteins that contribute to the identity of progeny cells. Many questions remain as to how this organization is maintained. In this study, we constructed strains of in which and the centromere can be induced to move to the opposite cell pole in the absence of chromosome replication, allowing us to ask whether once these chromosomal foci were positioned at the wrong pole, replication initiation and chromosome segregation can proceed in the opposite orientation. Our data reveal that DnaA can initiate replication and ParA can orchestrate segregation from either cell pole. The cell reconstructs the organization of its ParA gradient in the opposite orientation to segregate one replicated centromere from the new pole toward the stalked pole (i.e., opposite direction), while displaying no detectable viability defects. Thus, the unique polar microdomains exhibit remarkable flexibility in serving as a platform for directional chromosome segregation along the long axis of the cell. Bacteria can accomplish surprising levels of organization in the absence of membrane organelles by constructing subcellular asymmetric protein gradients. These gradients are composed of regulators that can either trigger or inhibit cell cycle events from distinct cell poles. In , the onset of chromosome replication and segregation from the stalked pole are regulated by asymmetric protein gradients. We show that the activators of chromosome replication and segregation are not restricted to the stalked pole and that their organization and directionality can be flipped in orientation. Our results also indicate that the subcellular location of key chromosomal loci play important roles in the establishment of the asymmetric organization of cell cycle regulators.
基因组的完整性对于细胞的存活至关重要。在细菌中，单一的圆形染色体在细胞中呈现出特定的取向，复制起点（）位于带有柄的细胞的极处。在复制起始时，复制的着丝粒样区域和迅速移动到相对的极处，在那里，由一个含有一组独特蛋白质的微域捕获，这些蛋白质有助于子细胞的身份识别。然而，关于这种组织如何维持，仍有许多问题尚未解决。在本研究中，我们构建了的菌株，在这些菌株中，和着丝粒可以在没有染色体复制的情况下被诱导移动到相反的细胞极，这使我们能够问，一旦这些染色体焦点位于错误的极处，复制起始和染色体分离是否可以沿着相反的方向进行。我们的数据表明，DnaA 可以起始复制，ParA 可以从任一细胞极协调分离。细胞以相反的方向重建其 ParA 梯度的组织，以将一个复制的着丝粒从新极分离到柄极（即相反的方向），同时没有检测到明显的生存缺陷。因此，独特的极性微域在作为沿着细胞长轴定向染色体分离的平台方面表现出显著的灵活性。细菌通过构建亚细胞不对称蛋白梯度，可以在没有膜细胞器的情况下实现惊人的组织水平。这些梯度由可以从不同细胞极触发或抑制细胞周期事件的调节剂组成。在中，从柄极开始的染色体复制和分离受到不对称蛋白梯度的调节。我们表明，染色体复制和分离的激活剂不限于柄极，它们的组织和方向性可以在方向上翻转。我们的结果还表明，关键染色体基因座的亚细胞位置在细胞周期调节剂不对称组织的建立中起着重要作用。
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