AbstractSmall regulatory RNAs (sRNAs) play a role in the control of bacterial virulence gene expression. In this study, we investigated an sRNA that was identified inStreptococcus pyogenes(group AStreptococcus, GAS) but is conserved throughout various streptococci. In a deletion strain, expression ofmga, the gene encoding the multiple virulence gene regulator, was reduced. Accordingly, transcript and proteome analyses revealed decreased expression of several Mga-activated genes. Therefore, and because the sRNA was shown to interact with the 5′ UTR of themgatranscript in a gel-shift assay, we designated it MarS formga-activatingregulatorysRNA. Down-regulation of important virulence factors, including the antiphagocytic M-protein, led to increased susceptibility of the deletion strain to phagocytosis and reduced adherence to human keratinocytes. In a mouse infection model, themarSdeletion mutant showed reduced dissemination to the liver, kidney, and spleen. Additionally, deletion ofmarSled to increased tolerance towards oxidative stress. Ourin vitroandin vivoresults indicate a modulating effect of MarS on virulence gene expression and on the pathogenic potential of GAS.