9357373 Kiley More than a century ago, Pasteur observed the profound effects of oxygen on cell metabolism. It is now known that oxygen has two major effects. First, excess oxygen can create reactive compounds that damage key molecules in cells, and secondly, too little oxygen may deplete energy resources vital for cell function. Although oxygen is known to play a pivotal role in cell physiology, little is known about the molecular mechanism(s) used by cells to sense and respond to changes in environmental oxygen concentrations. To begin to understand how this occurs, I will attempt to determine how the Escherichia coli transcription factor Fnr is activated by oxygen deprivation. The increase in Fnr activity under anaerobic conditions is critical for E. coli survival, since Fnr allows cells to adapt to anoxia by altering expression of genes involved in energy metabolism. Since Fnr levels are not oxygen regulated, a key problem is to identify the factor(s) which modulate its activity. Knowledge of such a factor(s) should ultimately allow dissection of the pathway for cellular oxygen sensing. In the present research program biochemical, genetic and physiological approaches will be used to learn how Fnr activity is regulated. Specifically, we wish to define the steps in Fnr activation, so that we may define how oxygen deprivation effects Fnr's conformational and oligomeric state(s), and then identify factors that regulate Fnr activity to gain insight into the pathway of cellular oxygen sensing. %%% Many cells require oxygen to grow and to metabolism. However, too much oxygen can kill cells, and too little oxygen can stop their growth. As a result, for a cell to survive and grow efficiently, there must be mechanisms which allow it to recognize oxygen and protect itself against changing concentrations of the gas in its environment. Escherichia coli, a bacterium, has a factor called Fnr, which may be involved in this detection system. This factor is formed in cells when too little oxygen is available to support cell growth. In the absence of oxygen, the factor appears to protect the cell by stopping the formation of certain enzymes ordinarily needed to form energy in air. The effect saves cell energy until oxygen again is available and growth resumes. Experiments in biochemistry, genetics and physiology will be performed to determine how oxygen influences the structure of Fnr and what other factor(s) might be involved in regulating its formation. ***
