Abstract
Phycobilisomes of the unicellular marine cyanobacteria are unique in having rod substructures with two distinct phycoerythrins, PE I and PE II, with five and six bilins, respectively (Ong, L. J., and Glazer, A. N. (1991) J. Biol. Chem. 266, 9515-9527). The genes for the alpha and beta subunits of PE I, PE II, and phycocyanin, and that for the PE II-associated linker polypeptide, are clustered on a single 15-kilobase region of the genome of Synechococcus sp. WH8020. Complete sequencing of this region allowed definitive assignment of the positions of all bilin attachment sites in these phycobiliproteins. Twelve other open reading frames are closely associated with the structural genes specified above. Six are homologous to open reading frames adjacent to phycobiliprotein genes in other cyanobacteria and inferred to be involved in bilin addition. This is the largest number of open reading frames of this class known in any cyanobacterium. Another of the open reading frames has a short region of striking similarity to the active site sequence of a bovine protein-phosphotyrosine phosphatase.
Highlights
From the Division of Biochemistry and Molecular Biology, Department ofMolecular and Cell Biology, University of California, Berkeley, California94720
In addition to the cy and p subunits of the phycobiliproteins, phycobilisomes contain linker polypeptides. These polypeptides function primarily inguiding the assembly of phycobilisome componentsand holding the complex together.The linker polypeptides of freshwater cyanobacteria do not carry bilins, whereas phycoerythrin-associated linker polypeptides of the marine unicellular cyanobacteria and of the red algae have covalently attached bilins [9,10,11]
The marine unicellular cyanobacteria constitute a significant portion of the total planktonic biomass in the oceans and contribute 5-25% of the primary productivity depending on the geographic location and season [12, 13]
Summary
Asinglephycocyanin inanyorganisme, xcept some chromaticadapters.ItcarriesPCBata-83, a-84,042, and0155. Protein and include one cluster of three (ORF200, ORF236, Structural Genes of the Phycobilisome Rod-Seven genes and ORF257) and two additional (ORF140 and ORF1961,' (mpeB, mpeA,mpeC, cpeB, cpeA, rpcB, and rpcA)encode none of which show similarity to any known sequence. The predicted protein en- respectively, found 3' of cpcA in several freshwater cyanobaccoded by ORF196 is too small (23 kDa) and acidic (PI 6.0) to teria [27, 29,30,31, 33, 46] The productsof the latter genes are fall within the range of normal linker polypeptides (27-35 required for the biosynthetic attachment of phycocyanobilin kDa andPI 8.0-9.2), nor does it show any sequence similarity to the a-Cys-8o4f C-phycocyanin [27,28,48]. C-PEb C-PEC with cpeZ and ORFZ suggested the sequence, PEW (LVYI)XRX(AS)(AV)(KR)(AGT)LGX(LIFM)(,theinitial
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