Summary of variation identified in the Sic protein among 1,673 serotype M1 GAS strains. Left: Positions of the polymorphic nucleotides and amino acids. The single-letter amino acid abbreviations are used. Far right: Domains of Sic located in the proximal half of the protein. SRR, short repeat region; R1–R3, repeats R1, R2, and R3. Modified from ref. 11with permission.