PARENT SESSION
Posters P2A Type I reaction centres. Abstracts (181-218)

Functional genomics of genes for biogenesis of Fe/S proteins in cyanobacteria. Gaozhong Shen^*,1, Ramakrishnan Balasubramanian¹, Tao Wang¹, Bhramara Tirupati¹, Martin Bollinger^{1, 2}, John Golbeck^{1, 2}, Donald Bryant¹, ¹ Department of Biochemistry & Molecular Biology, University Park, PA, USA² Department of Chemistry, University Park, PA, USA

ABSTRACT- Genomic sequencing of Synechocystis sp. PCC 6803 and other cyanobacteria has provided a useful tool in identifying genes with possible roles in the assembly of Fe/S clusters. Genes for two different systems of Fe/S cluster assembly (named SUF and ISC) have been identified in the genomes of several sequenced cyanobacteria. SufS and SufE are thought to be responsible for sulfur mobilization. SufC functions as a versatile orphan ATPase and may work together with the SufB and SufD proteins in iron assimilation and Fe/S cluster insertion. In cyanobacteria, SufR functions in the regulation of expression of the suf genes. We studied the functions of selected genes in the SUF and ISC systems in cyanobacteria using reverse genetics. No phenotype was observed for the iscS1 mutant of Synechococcus sp. PCC 7002, and the iscS1, iscS2 and fdx mutants of Synechocystis sp. PCC 6803. Indeed, the iscS1 iscS2 double mutant grows photoautotrophically. In contrast, we have not been able to produce fully segregated mutants of the sufD and sufS genes in Synechococcus sp. PCC 7002, or the sufS gene in Synechocystis sp. PCC 6803. This demonstrates that these suf genes are essential in cyanobacteria. Surprisingly, no phenotype could be observed in the sufA and iscA single mutants or in a sufA iscA double mutant of Synechococcus sp. PCC 7002. In contrast to what is currently believed for Azotobacter vinelandii, these results make it unlikely that IscA and SufA function as essential scaffolds in Fe/S cluster biogenesis in photosynthetic organisms. Components of the SUF system found in cyanobacteria are localized in the chloroplasts of higher plants. These results show that oxygenic photosynthetic organisms rely primarily on the SUF rather than the ISC system for biogenesis of Fe/S clusters for Photosystem I and/or other Fe/S proteins.

KEY WORDS: Photosystem I, cyanobacteria, Fe-S cluster, biogenesis