The important human pathogen Streptococcus pyogenes (group A Streptococcus [GAS]) produces a hyaluronic acid (HA) capsule that plays critical roles in immune evasion. Previous studies showed that the hasABC operon encoding the capsule biosynthesis enzymes is under the control of a single promoter, P1, which is negatively regulated by the two-component regulatory system CovR/S. In this work, we characterize the sequence upstream of P1 and identify a novel regulatory region controlling transcription of the capsule biosynthesis operon in the M1 serotype strain MGAS2221. This region consists of a promoter, P2, which initiates transcription of a novel small RNA, HasS, an intrinsic transcriptional terminator that inefficiently terminates HasS, permitting read-through transcription of hasABC, and a putative promoter which lies upstream of P2. Electrophoretic mobility shift assays, quantitative reverse transcription-PCR, and transcriptional reporter data identified CovR as a negative regulator of P2. We found that the P1 and P2 promoters are completely repressed by CovR, and capsule expression is regulated by the putative promoter upstream of P2. Deletion of hasS or of the terminator eliminates CovR-binding sequences, relieving repression and increasing read-through, hasA transcription, and capsule production. Sequence analysis of 44 GAS genomes revealed a high level of polymorphism in the HasS sequence region. Most of the HasS variations were located in the terminator sequences, suggesting that this region is under strong selective pressure. We discovered that the terminator deletion mutant is highly resistant to neutrophil-mediated killing and is significantly more virulent in a mouse model of GAS invasive disease than the wild-type strain. Together, these results are consistent with the naturally occurring mutations in this region modulating GAS virulence.

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Notes/Citation Information

Published in Infection and Immunity, v. 82, no. 12, p. 5293-5307.

Copyright © 2014, American Society for Microbiology. All Rights Reserved.

The copyright holders have granted the permission for posting the article here.

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Funding Information

This work was supported by NIH grants R21AI113253 from the NIAID and P20 RR020171 from the National Center for Research Resources (to N.K.), by NIH grant R01 AI087747 from the NIAID (to P.S.), and by Postdoctoral Fellowship 13POST16820024 from the American Heart Association (to M.F.). We also acknowledge the University of Kentucky Viral Production Core, which is partially supported by grant P20GM103486 from the National Institute of General Medical Sciences.

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Supplemental File: Tables S1-S6