D. J. BAST, V. NIZET, B. BEALL, V. DATTA, D. E. LOW, AND J. C. S. DE AZAVEDO. Department of Microbiology, Mount Sinai and Princess Margaret Hospitals, 600 University Avenue, Toronto, Ontario, Canada, M5G 1X5; University of California, San Diego, California, USA; Centers for Disease Control, Atlanta, Georgia, USA.

Background SLS is an oxygen-stable hemolysin produced by GAS. Although little is known about the molecular nature of SLS, our initial identification of sagA (SLS associated gene) supports the significance of this hemolysin in pathogenesis. In this study, we describe 8 additional open reading frames (ORF) immediately downstream of sagA also required for SLS production.

Methods ORF were identified by Tn917 mutagenesis and chromosome walking steps. Each ORF identified, was subsequently inactivated by homologous recombination and the resultant mutant examined both in vitro and in vivo for SLS production and virulence, respectively.

Results In addition to sagA, we identified 8 additional ORF’s associated with SLS production, 3 of which show homologies to proteins previously identified as antimicrobial peptide accessory proteins required for modification and transport. In particular, SAG-B shows homology to the microcin B17 processing enzyme (MBCA), while SAG-G shows homology to the ATP binding component of an ABC transporter. Reintroduction of sagA on a plasmid restored the b -hemolytic phenotype of a sagA mutant. The ability to complement sagA in trans, together with Northern blot analysis, suggest that the sagA message is independently transcribed, and that sagA may be the structural gene for SLS. Interestingly, although all SLS-deficient mutants persisted at the site of injection 5 days post-injection, all failed to produce necrotic lesions as seen with the wild-type organism.

Conclusions We conclude that sagA encodes for the precursor peptide of SLS and that a series of genes immediately downstream of sagA play a collective role in its modification to active SLS and transport.

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