Figure 1From: M-protein and other intrinsic virulence factors of Streptococcus pyogenes are encoded on an ancient pathogenicity islandCumulative GC skew (A) and TA skew (B) of the chromosome of the M1 S. pyogenes SF370. Cumulative skews (Y-axis, in nucleotide kilosteps) are represented along the chromosome (X-axis). Both skews are performed on one of the two strand of the streptococcal DNA double helix. The TA skew (B) reveals segments with steeper slopes referred to as steep-slope segments (SSRs) and revealing regions with different nucleotide composition. Phagic SSRs are represented by grey rectangles and numbered as they appear on the chromosome, while the conserved non-phagic SSR is outlined by a boxed orange rectangle. Virulence genes (blue dots) are spotted according to their position on the chromosome and the distance to the next virulence gene (right Y-axis, logarithmic scale). The overall average distance between virulence genes is 54.8 kb, except for a group of 10 genes (circled) present in the non-phagic 47-kb SSR for which the average distance is only 4.3 kb. This represents a ten-fold greater concentration of virulence factors compared to the rest of the chromosome.Back to article page