The POA subgraph surrounding the 450th amino acid in M. tuberculosis H37Rv rpoB (red dashed edges) captures extensive allelic diversity in other references (black edges). Grey squares represent nodes in the POA graph labeled with a base or an IUPAC code representing uncertainty about the base at that site (N: any base, Y: C or T). Edges are labeled with the number of genomes that share that edge. The bottom grey rectangles represent the H37Rv amino acid sequence.