Idealized M1 proteins on the GAS surface. (A) Surface expression of M1 protein by wild-type GAS 5448, GAS 5448 (Δemm1) carrying an empty plasmid or plasmids encoding wild-type M1, register 1-stabilized M1, or register 2-stabilized M1, as assayed by FACS, using a polyclonal anti-M1 protein antibody. The values are the means of three triplicates normalized to GAS 5448, with the SD shown. (B) Binding of FITC-labeled Fg to the same strains as in A as assayed by FACS. The values are normalized to the value for GAS 5448, with the SD shown.