The C. parvum nucleotide biosynthetic pathway is a phylogenetic mosaic. Enzymes labeled in red show strong phylogenetic association with eubacteria, those in green show association with plants and algae. Metabolic reconstruction and phylogenetic analyses presented here are based on the C. parvum type 2 IOWA genome [analysis of the type 1 data set () yielded identical results]. Supporting comparative genomic analyses are provided in . Two arrows indicate two or more enzymatic steps. Most nucleoside mono- and diphosphate kinase and phosphorylase steps have been omitted for simplicity. A complete set of these genes is present in the genome. The membrane topology of the feeder organelle () has been schematized. *, Transporter: the localization of nucleoside transporters is hypothetical, a localization outside the feeder organelle is equally possible. 1, adenosine transporter; 2, AK; 3, adenosine monophosphate deaminase; 4, IMPDH; 5, guanosine monophosphate synthase; 6, UK-UPRT; 7, uracil phosphoribosylltransferase; 8, TK; 9 ribonucleotide diphosphate reductase; 10, cytosine triphosphate synthetase; 11, deoxycytosine monophosphate deaminase; 12, dihydrofolate reductase-thymidylate synthase.