Tripartite toxin-antitoxin system regulates the production and release of pneumolysin by Streptococcus pneumoniae.

A tripartite regulatory system in Streptococcus pneumoniae links PlyA, PlyB, and PlyC to control pneumolysin (Ply) by destabilizing the Ply transcript.

• Why it matters: Pneumolysin is central to S. pneumoniae pathogenicity, but how the other ply operon genes regulate Ply production and release has been unclear.
• What they did: The study shows PlyA is a putative membrane-destabilising protein and PlyB/PlyC form a MazEF-like toxin-antitoxin system, with PlyC destabilising the Ply transcript.
• The result: A model proposes that high ply operon expression triggers membrane stress, negative feedback that degrades the PlyB antitoxin, releases PlyC, and degrades the ply transcript to tightly regulate Ply production.

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