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Infection and Immunity, November 2001, p. 7029-7038, Vol. 69, No. 11
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.11.7029-7038.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Generation and Surface Localization of Intact M Protein in Streptococcus pyogenes Are Dependent on sagA

Indranil Biswas, Pierre Germon,dagger Kathleen McDade, and June R. Scott*

Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia 30322

Received 15 June 2001/Returned for modification 27 July 2001/Accepted 20 August 2001

The M protein is an important surface-located virulence factor of Streptococcus pyogenes, the group A streptococcus (GAS). Expression of M protein is primarily controlled by Mga, a transcriptional activator protein. A recent report suggested that the sag locus, which includes nine genes necessary and sufficient for production of streptolysin S, another GAS virulence factor, is also needed for transcription of emm, encoding the M protein (Z. Li, D. D. Sledjeski, B. Kreikemeyer, A. Podbielski, and M. D. Boyle, J. Bacteriol. 181:6019-6027, 1999). To investigate this in more detail, we constructed an insertion-deletion mutation in sagA, the first gene in the sag locus, in the M6 strain JRS4. The resulting strain, JRS470, produced no detectable streptolysin S and showed a drastic reduction in cell surface-associated M protein, as measured by cell aggregation and Western blot analysis. However, transcription of the emm gene was unaffected by the sagA mutation. Detailed analysis with monoclonal antibodies and an antipeptide antibody showed that the M protein in the sagA mutant strain was truncated so that it lacks the C-repeat region and the C-terminal domain required for anchoring it to the cell surface. This truncated M protein was largely found, as expected, in the culture supernatant. Lack of surface-located M protein made the sagA mutant strain susceptible to phagocytosis. Thus, although sagA does not affect transcription of the M6 protein gene, it is needed for the surface localization of this important virulence factor.


* Corresponding author. Mailing address: Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA 30322. Phone: (404) 727-0402. Fax: (404) 727-8999. E-mail: scott{at}microbio.emory.edu.

dagger Present address: Station de Pathologie Aviaire et de Parasitologie, INRA---Centre de Tours, 37380 Nouzilly, France.


Infection and Immunity, November 2001, p. 7029-7038, Vol. 69, No. 11
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.11.7029-7038.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.



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