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Journal of Bacteriology, May 2001, p. 3065-3075, Vol. 183, No. 10
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.10.3065-3075.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

The CcrM DNA Methyltransferase of Agrobacterium tumefaciens Is Essential, and Its Activity Is Cell Cycle Regulated

Lyn Sue Kahng1,2 and Lucy Shapiro1,*

Department of Developmental Biology1 and Division of Gastroenterology, Department of Internal Medicine,2 Stanford University School of Medicine, Stanford, California

Received 21 December 2000/Accepted 2 March 2001

DNA methylation is now recognized as a regulator of multiple bacterial cellular processes. CcrM is a DNA adenine methyltransferase found in the alpha subdivision of the proteobacteria. Like the Dam enzyme, which is found primarily in Escherichia coli and other gamma proteobacteria, it does not appear to be part of a DNA restriction-modification system. The CcrM homolog of Agrobacterium tumefaciens was found to be essential for viability. Overexpression of CcrM is associated with significant abnormalities of cell morphology and DNA ploidy. Mapping of the transcriptional start site revealed a conserved binding motif for the global response regulator CtrA at the -35 position; this motif was footprinted by purified Caulobacter crescentus CtrA protein in its phosphorylated state. We have succeeded in isolating synchronized populations of Agrobacterium cells and analyzing their progression through the cell cycle. We demonstrate that DNA replication and cell division can be followed in an orderly manner and that flagellin expression is cyclic, consistent with our observation that motility varies during the cell cycle. Using these synchronized populations, we show that CcrM methylation of the chromosome is restricted to the late S phase of the cell cycle. Thus, within the alpha subdivision, there is a conserved cell cycle dependence and regulatory mechanism controlling ccrM expression.

* Corresponding author. Mailing address: Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA 94305. Phone: (650) 725-7678. Fax: (650) 725-7739. E-mail: shapiro{at}cmgm.stanford.edu.

Journal of Bacteriology, May 2001, p. 3065-3075, Vol. 183, No. 10
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.10.3065-3075.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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