 A variant of group A streptococcus erotype M1, UK, has been increasingly reported and can be differentiated from the global variant by its overexpression of the superantigen SPA. Here, Davies et al. probe the mechanism behind enhanced SPA expression and demonstrate that a SMP in the five-leader sequence of SSI is responsible for this virulent sphenotype. This article was authored by Marker Davies, Nadia Keller, Stefan Brower, and others.