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Journal of Bacteriology, November 2008, p. 7375-7381, Vol. 190, No. 22
0021-9193/08/$08.00+0     doi:10.1128/JB.01068-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Posttranslational Modification Influences the Effects of MgrA on norA Expression in Staphylococcus aureus{triangledown}

Que Chi Truong-Bolduc, Yanpeng Ding, and David C. Hooper*

Division of Infectious Diseases and Medical Services, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114-2696

Received 30 July 2008/ Accepted 5 September 2008

MgrA is a global regulator in Staphylococcus aureus. Differences in the effects of MgrA on norA expression have been reported for different strains, which varied in rsbU, a gene that affects the expression of sigB, which encodes an alternative {sigma} factor involved in stress responses. We hypothesized that MgrA was modified by sigB-dependent factors that affected its ability to control the expression of the norA efflux pump. Heterologously expressed MgrA purified from Escherichia coli was incubated with crude extracts (CE) from strains RN6390 (rsbU) and SH1000 (rsbU+) and tested for binding to the norA promoter. Purified MgrA exhibited greater binding to norA promoter DNA after being incubated with SH1000 CE than MgrA incubated with the RN6390 CE. Phosphorylation of MgrA occurring in cell extracts caused it to lose the ability to bind norA promoter DNA. Overexpression of pknB, encoding a candidate serine/threonine kinase, produced increased phospho-MgrA and led to a fivefold increase in the transcript level of norA for both RN6390 and SH1000, as well as a fourfold increase in the MICs of norfloxacin and ciprofloxacin for these two strains. The levels of expression of pknB in RN6390 and SH1000, however, indicated that additional factors related to rsbU or sigB contribute to the differential regulatory effects of MgrA on norA expression.

* Corresponding author. Mailing address: Division of Infectious Diseases, Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114-2696. Phone: (617) 726-3812. Fax: (617) 726-7416. E-mail: dhooper{at}partners.org

{triangledown} Published ahead of print on 19 September 2008.

Journal of Bacteriology, November 2008, p. 7375-7381, Vol. 190, No. 22
0021-9193/08/$08.00+0     doi:10.1128/JB.01068-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



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