Reisinger Sarah J, Huntwork Sarah, Viollier Patrick H, Ryan Kathleen R
Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, California 94720, USA.
J Bacteriol. 2007 Nov;189(22):8308-20. doi: 10.1128/JB.00868-07. Epub 2007 Sep 7.
The Caulobacter cell cycle is regulated by a network of two-component signal transduction proteins. Phosphorylation and stability of the master transcriptional regulator CtrA are controlled by the CckA-ChpT phosphorelay, and CckA activity is modulated by another response regulator, DivK. In a screen to identify suppressors of the cold-sensitive divK341 mutant, we found point mutations in the essential gene divL. DivL is similar to histidine kinases but has a tyrosine instead of a histidine at the conserved phosphorylation site (Y550). Surprisingly, we found that the ATPase domain of DivL is not essential for Caulobacter viability. We show that DivL selectively affects CtrA phosphorylation but not CtrA proteolysis, indicating that DivL acts in a pathway independent of the CckA-ChpT phosphorelay. divL can be deleted in a strain overproducing the phosphomimetic protein CtrAD51E, but unlike DeltactrA cells expressing CtrAD51E, this strain is profoundly impaired in the control of chromosome replication and cell division. Thus, DivL performs a second function in addition to promoting CtrA phosphorylation. DivL is required for bipolar DivK localization and positively regulates DivK phosphorylation. Our results show that DivL controls two key cell cycle regulators, CtrA and DivK, and that phosphoryl transfer is not DivL's essential cellular activity.
柄杆菌的细胞周期受双组分信号转导蛋白网络调控。主转录调节因子CtrA的磷酸化和稳定性由CckA-ChpT磷酸中继控制，而CckA的活性则受另一种应答调节因子DivK的调节。在一项旨在鉴定冷敏感型divK341突变体抑制子的筛选中，我们在必需基因divL中发现了点突变。DivL与组氨酸激酶相似，但在保守的磷酸化位点（Y550）有一个酪氨酸而非组氨酸。令人惊讶的是，我们发现DivL的ATP酶结构域对柄杆菌的生存力并非必需。我们表明DivL选择性地影响CtrA的磷酸化，但不影响CtrA的蛋白水解，这表明DivL在一条独立于CckA-ChpT磷酸中继的途径中发挥作用。在过量表达磷酸模拟蛋白CtrAD51E的菌株中可以缺失divL，但与表达CtrAD51E的DeltactrA细胞不同，该菌株在染色体复制和细胞分裂的控制方面严重受损。因此，DivL除了促进CtrA磷酸化外还执行第二种功能。DivL是双极DivK定位所必需的，并正向调节DivK的磷酸化。我们的结果表明DivL控制两个关键的细胞周期调节因子CtrA和DivK，并且磷酸转移不是DivL的必需细胞活性。
