As models for gene regulation and transport processes, microbial systems offer distinct advantages over other organisms. These advantages include fast growth rates and versatile genetics and selection techniques.

Biogenesis of extracellular components. Our group studies the assembly of cytochrome c in photosynthetic bacteria and pathogens such as Bordetella. We have isolated bacterial mutants and genes involved in this assembly process, which occurs outside the cytoplasmic membrane. The model we have developed for this process includes an ATP-dependent heme export system homologous to membrane translocators like the cystic fibrosis protein. Other components that are predicted to function as periplasmic heme and apocytochrome chaperones and thiol reduction proteins are under investigation. General processes that occur in all organisms for which these studies are relevant include mechanisms of heme and iron transport, disulfide bond formation and reduction, and protein folding and secretion.

Gene regulatory studies. Photosynthetic microorganisms possess the ability to adapt metabolically to a wide range of growth conditions in nature. This capacity to convert from one mode to another is facilitated by complex regulatory systems that respond to changes in their environment. Our research is directed toward understanding these capabilities of photosynthetic bacteria, with particular emphasis on the genes for nitrogen and photosynthetic control. We have obtained mutants in and have cloned regulatory genes, both negative and positive activators, that respond to oxygen and nitrogen availability. The regulatory cascades along with the transcriptional machinery have been reconstituted in vitro for detailed studies.

Plant gene regulation. We are using GFP, LUC, and GUS-based enhancer trap screens to discover genes that are regulated by nitrogen starvation and other environmental stresses. These reporters are then used to investigate the regulatory cascades involved in these responses.

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