DEFECTIVE EXPORT OF A PERIPLASMIC ENZYME DISRUPTS REGULATION OF FATTY-ACID SYNTHESIS

Escherichia coli thioesterase I (TesA) encoded by the tesA gene is loc ated in the cellular periplasm. The tesA gene was modified by deletion of the leader sequence such that the mature enzyme was instead locali zed to the cellular cytosol. Production of thioesterase I in the cytos ol results in striking changes in the pattern of E. coli lipid synthes is. In contrast to normal E. coli cells, cells producing cytosolic Tes A synthesize large amounts of free fatty acid at all stages of growth. Moreover, cultures of the cytosolic TesA-producing strain continue li pid synthesis (as free fatty acid) in stationary phase whereas lipid s ynthesis is normally strongly inhibited in such cultures. Surprisingly , production of cytosolic thioesterase I gave only modest inhibition o f membrane phospholipid synthesis. These results demonstrate that inte rnalization of a normally secreted enzyme can disrupt normal cellular regulatory mechanisms.