THE GENE FOR GAMMA-GLUTAMYLCYSTEINE SYNTHETASE FROM THIOBACILLUS-FERROOXIDANS HAS LOW HOMOLOGY TO ITS ESCHERICHIA-COLI EQUIVALENT AND IS LINKED TO THE GENE FOR CITRATE SYNTHASE

The gene for gamma-glutamylcysteine synthetase (gshA) from Thiobacillu s ferrooxidans was isolated from a family of cosmids by its ability to complement an Escherichia coli gshA trxA double mutant which was unab le to grow on minimal medium lacking glutathione. The predicted sequen ce of the gamma-glutamylcysteine synthetase was found to have only 18% amino acid sequence identity to the equivalent enzyme from E. coli. I n spite of this low sequence homology, concentrations of GSH in a cell extract prepared from the E. coli gshA trxA mutant containing the clo ned gene were almost as high as in a cell extract prepared from a wild -type E. coli strain. The gshA gene was found to be physically and tra nscriptionally linked to the T. ferrooxidans gene for citrate synthase (gltA). The T. ferrooxidans and E. coli citrate synthases shared 37 % amino acid sequence identity and the cloned T. ferrooxidans citrate s ynthase gene was able to complement an E. coli gltA mutant.