Oteins including the plant and Prochlorococcus enzymes responsible for the synthesis of Chl b from chlorophyllide a, chlorophyllide a oxygenase (CAO) (Fig. 2) (31). Five putative proteins containing a CAO-type Rieske-FeS motif are encoded by A. marina. Most of the candidate genes in A. marina fall into orthologous clusters with other hypothetical cyanobacterial proteins (Fig. 2). Only one protein,