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Journal of Bacteriology, November 2007, p. 8308-8320, Vol. 189, No. 22
0021-9193/07/$08.00+0     doi:10.1128/JB.00868-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

DivL Performs Critical Cell Cycle Functions in Caulobacter crescentus Independent of Kinase Activity{triangledown}

Sarah J. Reisinger,1 Sarah Huntwork,2,{dagger} Patrick H. Viollier,3 and Kathleen R. Ryan1*

Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, California 94720,1 Department of Developmental Biology, Stanford University School of Medicine, Stanford, California 94305,2 Department of Molecular Biology and Microbiology, Case Western Reserve University School of Medicine, Cleveland, Ohio 441063

Received 4 June 2007/ Accepted 28 August 2007

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 {Delta}ctrA 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.

* Corresponding author. Mailing address: University of California, Berkeley, Department of Plant and Microbial Biology, 251 Koshland Hall, Berkeley, CA 94720. Phone: (510) 642-5559. Fax: (510) 642-4995. E-mail: kryan{at}nature.berkeley.edu

{triangledown} Published ahead of print on 7 September 2007.

{dagger} Present address: Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139.

Journal of Bacteriology, November 2007, p. 8308-8320, Vol. 189, No. 22
0021-9193/07/$08.00+0     doi:10.1128/JB.00868-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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