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Journal of Bacteriology, February 2001, p. 921-927, Vol. 183, No. 3
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.3.921-927.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Lowering S-Adenosylmethionine Levels in Escherichia coli Modulates C-to-T Transition Mutations

Georgina Macintyre,* C. Victoria Atwood, and Claire G. Cupples

Biology Department, Concordia University, Montreal, Quebec H3G 1M8, Canada

Received 21 August 2000/Accepted 10 November 2000

Deoxycytosine methylase (Dcm) enzyme activity causes mutagenesis in vitro either directly by enzyme-induced deamination of cytosine to uracil in the absence of the methyl donor, S-adenosylmethionine (SAM), or indirectly through spontaneous deamination of [5-methyl]cytosine to thymine. Using a Lac reversion assay, we investigated the contribution of the first mechanism to Dcm mutagenesis in vivo by lowering the levels of SAM. Escherichia coli SAM levels were lowered by reducing SAM synthetase activity via the introduction of a metK84 allele or by hydrolyzing SAM using the bacteriophage T3 SAM hydrolase. The metK84 strains exhibited increased C-to-T mutagenesis. Expression of the T3 SAM hydrolase gene, under the control of the arabinose-inducible PBAD promoter, effectively reduced Dcm-mediated genomic DNA methylation. However, increased mutagenesis was not observed until extremely high arabinose concentrations were used, and genome methylation at Dcm sites was negligible.

* Corresponding author. Mailing address: Biology Department, Concordia University, 1455 de Maisonneuve Blvd., W., Montreal, Quebec H3G 1M8, Canada. Phone: (514) 848-4026. Fax: (514) 848-2881. E-mail ginmac{at}vax2.concordia.ca.

Journal of Bacteriology, February 2001, p. 921-927, Vol. 183, No. 3
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.3.921-927.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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