Proposed organization of nan gene clusters in selected streptococci. Canonical nan genes in S. pneumoniae strains D39, ATCC700669 and TIGR4, and GBS S. agalactiae have the same color designations as given in the legend to Figure 5, with the addition of Axe (magenta), YjhC (grey), and YjhB (gold) based on orthologs of E. coli genes described in the text. The known or proposed functions of other genes in the various clusters are listed above the open arrows. The numbers below at left or right of the first or last gene in the cluster gives the beginning and ending nucleotide positions of each gene segment.