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Nature. 2009 Sep 10;461(7261):258-262. doi: 10.1038/nature08284. Epub 2009 Aug 26.

Photosystem I gene cassettes are present in marine virus genomes.

Author information

Faculty of Biology, Technion - Israel Institute of Technology, Haifa 32000, Israel.
Faculty of Computer Science, Technion - Israel Institute of Technology, Haifa 32000, Israel.
Department of Biology, San Diego State University, San Diego 92182, California, USA.
Center for Microbial Sciences, San Diego State University, San Diego 92182, California, USA.
Bioinformatics Knowledge Unit, Lorry I. Lokey Interdisciplinary Center for Life Sciences and Engineering, Technion - Israel Institute of Technology, Haifa 32000, Israel.
CNRS and UPMC-Université Paris 6 (UMR 7144), Station Biologique, 29682 Roscoff, France.
National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA.
Department of Biochemistry, George S. Wise Faculty of Life Sciences, Daniella Rich Institute for Structural Biology, Tel Aviv University, Tel Aviv 69978, Israel.
Contributed equally


Cyanobacteria of the Synechococcus and Prochlorococcus genera are important contributors to photosynthetic productivity in the open oceans. Recently, core photosystem II (PSII) genes were identified in cyanophages and proposed to function in photosynthesis and in increasing viral fitness by supplementing the host production of these proteins. Here we show evidence for the presence of photosystem I (PSI) genes in the genomes of viruses that infect these marine cyanobacteria, using pre-existing metagenomic data from the global ocean sampling expedition as well as from viral biomes. The seven cyanobacterial core PSI genes identified in this study, psaA, B, C, D, E, K and a unique J and F fusion, form a cluster in cyanophage genomes, suggestive of selection for a distinct function in the virus life cycle. The existence of this PSI cluster was confirmed with overlapping and long polymerase chain reaction on environmental DNA from the Northern Line Islands. Potentially, the seven proteins encoded by the viral genes are sufficient to form an intact monomeric PSI complex. Projection of viral predicted peptides on the cyanobacterial PSI crystal structure suggested that the viral-PSI components might provide a unique way of funnelling reducing power from respiratory and other electron transfer chains to the PSI.

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