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R plants also synthesize both - and -carotene; however, -carotene is used primarily as a precursor of lutein, and only -carotene is found in reaction centers. Future biochemical work may indicate whether a preferential interaction between Chl d and -carotene (rather than -carotene) could account for its exclusivity in the reaction center. The chromosome of A. marina codes for 11 proteins predicted
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Rently free to specialize their metabolic library.ATP Synthase. One interesting case of the idiosyncratic plasmidgene library in A. marina is the inclusion of a second full set of ATP synthase genes on plasmid pREB4 (AM1 D0157-67). These genes are arranged into a unique operon and the individual proteins do not clearly fit into any of the described families (SI Fig. 5) (25). This unusual operon is
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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,
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Ed transposable regions for 20 of the genes, significantly lower than the 70 found in Nostoc sp. PCC7120 (2). This is partly because of the vast disparity in transposable elements in the two similarly sized genomes, with nearly 1,300 detected in Nostoc and only 500 in A. marina. Surprisingly, a large number of transposases and integrases in A. marina cluster together in regions with no detectabl
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Ed transposable regions for 20 of the genes, significantly lower than the 70 found in Nostoc sp. PCC7120 (2). This is partly because of the vast disparity in transposable elements in the two similarly sized genomes, with nearly 1,300 detected in Nostoc and only 500 in A. marina. Surprisingly, a large number of transposases and integrases in A. marina cluster together in regions with no detectabl
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Ecies (32). Such enzymes could provide another means for Chl d biosynthesis. A. marina codes for 12 proteins with putative radical SAM motifs, far more than expected from an oxygen-producing cyanobacterium. Of these 12, two (AM1 5023 and AM1 5798) share very little homology with other sequenced cyanobacteria. The Chl d biosynthesis pathway may not be as simple as expected. Unlike the formyl side c
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Ed in Na -transport. However, it is clear that this class of ATP synthase does not share any greater degree of similarity to Na -transport systems in Ilyobacter tartaricus and others (27) than to other ATP synthases. The primary sequences of these proteins are so divergent from other ATP synthases that a thorough biochemical study is needed to confidently propose a functional role.Chlorophyll Bios
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Ed in Na -transport. However, it is clear that this class of ATP synthase does not share any greater degree of similarity to Na -transport systems in Ilyobacter tartaricus and others (27) than to other ATP synthases. The primary sequences of these proteins are so divergent from other ATP synthases that a thorough biochemical study is needed to confidently propose a functional role.Chlorophyll Bios