Distribution of the four genes in the taxa sampled in this study. A hypothetical tree of eukaryotes for which genomes have been fully sampled and published, *; is close to completion, **; or only partially sampled (genome sequence survey or expressed sequence tags), ***; indicating their classification into "super-groups" [29-31], showing the presence or absence of the four genes in the study. Please notice that the gene absences in the genomes that are close to completion are unconfirmed, they may turn into presences upon publication. A and B refer to strongly separated groups in the phylogenetic analyses, as indicated in Figures 2-4 & 6. The priS genes encode the hybrid-cluster proteins, fprA genes encode the A-type flavoproteins, nagB genes encode glucosamine-6-phosphate isomerase proteins and the adhE genes encode the alcohol dehydrogenase E proteins.