Functions of the CckA histidine kinase in Caulobacter cell cycle control

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271

Temporally and spatially controlled master regulators drive the Caulobacter cell cycle by regulating the expression of >200 genes. Rapid clearance of the master regulator, CtrA, by the ClpXP protease is a critical event that enables the initiation of chromosome replication at specific times in the cell cycle. We show here that a previously unidentified single domain-response regulator, CpdR, when in the unphosphorylated state, binds to ClpXP and, thereby, causes its localization to the cell pole. We further show that ClpXP localization is required for CtrA proteolysis. When CpdR is phosphorylated, ClpXP is delocalized, and CtrA is not degraded. Both CtrA and CpdR are phosphorylated via the same CckA histidine kinase phospho-signaling pathway, providing a reinforcing mechanism that simultaneously activates CtrA and prevents its degradation by delocalizing the CpdR͞ClpXP complex. In swarmer cells, CpdR is in the phosphorylated state, thus preventing ClpXP localization and CtrA degradation. As swarmer cells differentiate into stalked cells (G1͞S transition), unphosphorylated CpdR accumulates and is localized to the stalked cell pole, where it enables ClpXP localization and CtrA proteolysis, allowing the initiation of DNA replication. Dynamic protease localization mediated by a phosphosignaling pathway is a novel mechanism to integrate spatial and temporal control of bacterial cell cycle progression.Caulobacter ͉ ClpXP ͉ phosphorylation ͉ proteolysis ͉ temporal control

Section: Phosphorylation Of Ctra and Cpdr By A Common Ccka Histidine mentioning

confidence: 55%

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confidence: 77%

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A phospho-signaling pathway controls the localization and activity of a protease complex critical for bacterial cell cycle progression

Iniesta¹,

McGrath

Reisenauer³

et al. 2006

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188

271

“…Because two-component systems generally sense and respond to transitory environmental signals (3)(4)(5)(6)(7), it is unusual for histidine kinases and response regulators to be essential for viability. Caulobacter has several essential two-component systems, including CenK/CenR, which controls cell envelope biogenesis and integrity (8), and CckA/ChpT/CtrA, which regulates cell cycle progression (9)(10)(11)(12) in a fashion analogous to eukaryotic cyclin-dependent kinases (13).…”

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confidence: 99%

Cell pole–specific activation of a critical bacterial cell cycle kinase

Iniesta

Hillson²,

Shapiro³

2010

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114

Caulobacter crescentus integrates phospho-signaling pathways and transcription factor regulatory cascades to drive the cell cycle. Despite the essential role of the CckA histidine kinase in the control of cell cycle events, the factors that signal its activation at a specific time in the cell cycle have remained elusive. A conditional genetic screen for CckA mislocalization mutants, using automated fluorescence microscopy and an image processing platform, revealed that the essential DivL protein kinase promotes CckA localization, autophosphorylation, and activity at the new cell pole. The transient accumulation of DivL at the new cell pole, but not its kinase activity, is required for the localization and activation of CckA. Because DivL and CckA accumulate at the same cell pole after the initiation of DNA replication and were found to interact in vivo, we propose that DivL recruits CckA to the pole, thereby promoting its autophosphorylation and activity.

“…However, CtrA also represses chromosome replication by binding to five sites within the replication origin (7). Because CtrA has multiple functions, its activity is tightly controlled by three mechanisms: cell cycleregulated transcription (8), cell cycle-regulated phosphorylation (9,10), and rapid proteolysis at the SW-ST transition and in the stalked compartment of the predivisional cell (9). These processes ensure that CtrA activity is present in swarmer and predivisional cells, but absent in stalked cells preparing to enter S phase.…”

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confidence: 99%

Recruitment of a cytoplasmic response regulator to the cell pole is linked to its cell cycle-regulated proteolysis

Ryan

Huntwork

Shapiro

2004

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The response regulator CtrA, which silences the Caulobacter origin of replication and controls multiple cell cycle events, is specifically proteolyzed in cells preparing to initiate DNA replication. At the swarmer-to-stalked cell transition and in the stalked compartment of the predivisional cell, CtrA is localized to the cell pole just before its degradation. Analysis of the requirements for CtrA polar localization and CtrA proteolysis revealed that both processes require a motif within amino acids 1-56 of the CtrA receiver domain, and neither process requires CtrA phosphorylation. These results strongly suggest that CtrA polar localization is coupled to its cell cycle-regulated proteolysis. The polarly localized DivK response regulator promotes CtrA localization and proteolysis, but it does not directly recruit CtrA to the cell pole. Mutations in the divJ and pleC histidine kinases perturb the characteristic asymmetry of CtrA localization and proteolysis in the predivisional cell. We propose that polar recruitment of CtrA evolved to ensure that CtrA is degraded only in the stalked half of the predivisional cell, perhaps by localizing a proteolytic adaptor protein to the stalked pole. This is an example of controlled proteolysis of a cytoplasmic protein that is associated with its active recruitment to a specific subcellular address.Caulobacter ͉ CtrA ͉ ClpXP I n Caulobacter crescentus, DNA replication occurs once per cell division, and the phases of the cell cycle are linked to observable morphological changes (reviewed in refs. 1 and 2). Motile swarmer cells (Fig. 1) in the G 1 phase of the cell cycle develop into stalked cells ( Fig. 1) and initiate chromosome replication. During the swarmer-to-stalked cell (SW-ST) (or G 1 -S) transition, each cell sheds its polar flagellum and builds a stalk at the same site. As DNA replication proceeds, stalked cells elongate and become predivisional cells with distinct poles. A new flagellum is built at the pole opposite the stalk, so that each cell division produces a motile swarmer cell and a stalked cell. Before cell separation, a diffusion barrier is established between the swarmer and stalked compartments of the predivisional cell so that they contain distinct sets of signal transduction proteins that yield progeny with different replicative fates (3): the stalked progeny can initiate DNA replication immediately, whereas the swarmer cell must first differentiate into a new stalked cell.A key signal transduction protein that regulates Caulobacter cell cycle progression is the essential response regulator CtrA (4). CtrA directly induces or represses the transcription of Ϸ55 operons in the Caulobacter genome, including genes needed for flagellum and pili biosynthesis, DNA methylation, cell division, chemotaxis, and metabolism (5, 6). However, CtrA also represses chromosome replication by binding to five sites within the replication origin (7). Because CtrA has multiple functions, its activity is tightly controlled by three mechanisms: cell cycleregulated transcription (...