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Genetic organization of the sigX1 and sigX2 loci. Shown are 9-kb segments of GAS DNA surrounding sigX1 (A) and sigX2 (B) from M1 strain SF370. The two sigX genes are represented by black arrows. Six kilobases of sequence upstream of sigX are conserved for each copy of the two genes and contain two of the six rRNA operons. The sequence downstream from each copy of sigX is unique at each locus. IS1548 is present in all three sequenced strains but not in JRS4.
