ITS Phylogeny of Prochlorococcus and Synechococcus showing gene order surrounding FBA I locus. Phylogeny of Prochlorococcus and Synechococcus strains showing the distribution of class I and class II FBA. Maximum likelihood tree based on rRNA ITS sequences with bootstrap support shown for major nodes with greater than 70% support. The branch leading to one clade of Prochlorococcus (indicated by double hatch marks) has been truncated to fit. The genomic context of FBA genes is shown for completely sequenced genomes. Class I FBA (eukaryotic) is shown in red and class II (prokaryotic) is shown in green. Black arrows correspond to up and downstream genes that are conserved in order and direction in most genomes, whereas grey arrows are the few exceptions to this conservation.