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Journal of Bacteriology, August 2003, p. 4410-4417, Vol. 185, No. 15
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.15.4410-4417.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Characterization of Staphylococcus aureus SarA Binding Sites

Kristen M. Sterba,1 Samuel G. Mackintosh,1 Jon S. Blevins,2,{dagger} Barry K. Hurlburt,1,3 and Mark S. Smeltzer2*

Departments of Biochemistry and Molecular Biology,1 Microbiology and Immunology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205,2 Southern Regional Research Center, United States Department of Agriculture, New Orleans, Louisiana 701243

Received 13 February 2003/ Accepted 28 April 2003

The staphylococcal accessory regulator locus (sarA) encodes a DNA-binding protein (SarA) that modulates expression of over 100 genes. Whether this occurs via a direct interaction between SarA and cis elements associated with its target genes is unclear, partly because the definitive characteristics of a SarA binding site have not been identified. In this work, electrophoretic mobility shift assays (EMSAs) were used to identify a SarA binding site(s) upstream of the SarA-regulated gene cna. The results suggest the existence of multiple high-affinity binding sites within the cna promoter region. Using a SELEX (systematic evolution of ligands by exponential enrichment) procedure and purified, recombinant SarA, we also selected DNA targets that contain a high-affinity SarA binding site from a random pool of DNA fragments. These fragments were subsequently cloned and sequenced. Randomly chosen clones were also examined by EMSA. These DNA fragments bound SarA with affinities comparable to those of recognized SarA-regulated genes, including cna, fnbA, and sspA. The composition of SarA-selected DNAs was AT rich, which is consistent with the nucleotide composition of the Staphylococcus aureus genome. Alignment of selected DNAs revealed a 7-bp consensus (ATTTTAT) that was present with no more than one mismatch in 46 of 56 sequenced clones. By using the same criteria, consensus binding sites were also identified upstream of the S. aureus genes spa, fnbA, sspA, agr, hla, and cna. With the exception of cna, which has not been previously examined, this 7-bp motif was within the putative SarA binding site previously associated with each gene.


* Corresponding author. Mailing address: Department of Microbiology and Immunology, Mail Slot 511, University of Arkansas for Medical Sciences, Little Rock, AR 72205. Phone: (501) 686-7958. Fax: (501) 686-5359. E-mail: smeltzermarks{at}uams.edu.

{dagger} Present address: Department of Microbiology and Immunology, University of Texas Southwestern Medical Center, Dallas, Tex.


Journal of Bacteriology, August 2003, p. 4410-4417, Vol. 185, No. 15
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.15.4410-4417.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.




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