Research Summary

We study the molecular genetics of nitrogen fixation and cellular differentiation in cyanobacteria as well as genes encoding the enzyme acetyl-CoA carboxylase (ACC) in plants, in apicomplexan parasites and in humans. The cyanobacterium Anabaena grows in filaments of 100 cells or more. When starved for nitrogen, specialized cells called heterocysts differentiate from the photosynthetic vegetative cells at regular intervals along each filament. Heterocysts are anaerobic factories for nitrogen fixation; in them, the nitrogenase enzyme complex is synthesized and the oxygen-evolving photosystem II is turned off. More than 1000 genes are differentially expressed during the irreversible development of heterocysts from vegetative cells. We have sequenced genes for nitrogen fixation, for components of the photosynthetic apparatus and for the sigma and core subunits of RNA polymerase. Among mutants unable to fix nitrogen aerobically are some with altered heterocyst pattern or morphology. We have used complementation to isolate the genes defective in many of these mutants. They encode proteins that participate in environment-sensing regulatory cascades. The relationships among these regulatory proteins are being studied using the Green Fluorescent Protein as a cell-specific reporter of gene expression. Fatty acid synthesis begins in all organisms with the reaction catalyzed by ACC. In chicken, rat, yeast and plants all of the ACC domains reside in a single polypeptide. Yeast cells expressing wheat ACC are sensitive to herbicides that target the enzyme. Yeast expressing chimeras of the cytoplasmic and chloroplast form of the wheat ACC permit determination of the amino acid residues responsible for herbicide binding. We also have yeast strains expressing active ACC from Toxoplasma gondii, suitable for screening for new inhibitors of the parasite. Current experiments have constructed yeast strains expressing active human ACC, which serve in screens for new drugs for obesity.

Selected Publications

Zuther, E., Huang, S., Jelenska, J., Eilenberg, H., Arnold, E. M., Su, X., Sirikhachornkit, A., Podkowinski, J., Zilberstein, A., Haselkorn, R. and Gornicki, P. (2004). "Complex nested promoters control tissue-specific expression of acetyl-CoA carboxylase genes in wheat." Proc Natl Acad Sci U S A 101: 1403-8. (PubMed)

Rouhiainen, L., Vakkilainen, T., Siemer, B. L., Buikema, W., Haselkorn, R. and Sivonen, K. (2004). "Genes coding for hepatotoxic heptapeptides (microcystins) in the cyanobacterium Anabaena strain 90." Appl Environ Microbiol 70: 686-92. (PubMed)

Podkowinski, J., Jelenska, J., Sirikhachornkit, A., Zuther, E., Haselkorn, R. and Gornicki, P. (2003). "Expression of cytosolic and plastid acetyl-coenzyme A carboxylase genes in young wheat plants." Plant Physiol 131: 763-72. (PubMed)

Kapatral, V., Anderson, I., Ivanova, N., Reznik, G., Los, T., Lykidis, A., Bhattacharyya, A., Bartman, A., Gardner, W., Grechkin, G., Zhu, L., Vasieva, O., Chu, L., Kogan, Y., Chaga, O., Goltsman, E., Bernal, A., Larsen, N., D'Souza, M., Walunas, T., Pusch, G., Haselkorn, R., Fonstein, M., Kyrpides, N. and Overbeek, R. (2002). "Genome sequence and analysis of the oral bacterium Fusobacterium nucleatum strain ATCC 25586." J Bacteriol 184: 2005-18. (PubMed)

Ivanova, N., Sorokin, A., Anderson, I., Galleron, N., Candelon, B., Kapatral, V., Bhattacharyya, A., Reznik, G., Mikhailova, N., Lapidus, A., Chu, L., Mazur, M., Goltsman, E., Larsen, N., D'Souza, M., Walunas, T., Grechkin, Y., Pusch, G., Haselkorn, R., Fonstein, M., Ehrlich, S. D., Overbeek, R. and Kyrpides, N. (2003). "Genome sequence of Bacillus cereus and comparative analysis with Bacillus anthracis." Nature 423: 87-91. (PubMed)

Jones, K. M., Buikema, W. J. and Haselkorn, R. (2003). "Heterocyst-specific expression of patB, a gene required for nitrogen fixation in Anabaena sp. strain PCC 7120." J Bacteriol 185: 2306-14. (PubMed)

Kapatral, V., Ivanova, N., Anderson, I., Reznik, G., Bhattacharyya, A., Gardner, W. L., Mikhailova, N., Lapidus, A., Larsen, N., D'Souza, M., Walunas, T., Haselkorn, R., Overbeek, R. and Kyrpides, N. (2003). "Genome analysis of F. nucleatum sub spp vincentii and its comparison with the genome of F. nucleatum ATCC 25586." Genome Res 13: 1180-9. (PubMed)

Luke, K., Radek, A., Liu, X., Campbell, J., Uzan, M., Haselkorn, R. and Kogan, Y. (2002). "Microarray analysis of gene expression during bacteriophage T4 infection." Virology 299: 182-91. (PubMed)