Studies of the productivity and maintenance of cell functions in the stationary-phase cells of bacteria

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This research project was aimed to clarify the relationship between structure and function of sigma^<38> protein which functions specifically in the stationary phase of E.coli, and to know the properties of sigma^<38> protein in the amino acid-producing cells. The results obtained are as follows : (1) A derivative of sigma^<38> which has deleted the region 4.2 retained a higher activity than the original sigma^<38>, indicating that the region 4.2 has a function to moderate the activity. (2) In the culture of amino acid-producing E.coli cells (threonine production), the level of sigma^<38> protein increased rapidly in the first 3 to 5 hr cultivation, then settled down to a lower level at 10-20hr, and increased again afterward Amino acid productivity estimated by the conversion efficiency of carbon source to amino acid was highest at 20 hr cultivation and then decreased. These results indicate that the critical time for efficient production of amino acid can be pointed by monitoring the level of sigma^<38> protein in the cells.