The reduction of atmospheric nitrogen to ammonia, termed nitrogen fixation, is inhibited by oxygen; hence, oxygen-evolving photosystem II and nitrogen fixation cannot coexist. Some of the filamentous cyanobacteria, which have photosystem II, can differentiate cells, called heterocysts, that are specialized for nitrogen fixation. Many structural and biochemical changes occur during heterocyst differentiation, including loss of photosystem II (PSII) activity. Dr. Thiel will study the mechanism of inactivation of the components of this photosystem during heterocyst differentiation. She will identify in a heterocyst- forming cyanobacterium the genes for PSII components by Southern hybridization and the protein components of PSII by Western blots, and will study the regulation of transcription of these genes and the turnover of these proteins during heterocyst differentiation. These studies should provide information on the cellular mechanisms that allow an organism that has oxygen evolving PSII to also fix nitrogen. Dr. Thiel will team teach courses in Microbiology and in Bioenergetics, give lectures in graduate seminar courses, and direct the research of graduate students. She will also give formal seminars and have informal discussions on opportunities for women in science through the Women's Resource Center at Washington University. This project furthers VPW program objectives which are (1) to provide opportunities for women to advance their careers in engineering and in the disciplines of science supported by NSF and (2) to encourage women to pursue careers in science and engineering by providing greater visibility for women scientists and engineers employed in industry, government, and academic institutions. By encouraging the participation of women in science, it is a valuable investment in the Nation's future scientific vitality.
