%0 Journal Article %A Denk, Dagmar %A Böck, August %T l-Cysteine Biosynthesis in Escherichia coli: Nucleotide Sequence and Expression of the Serine Acetyltransferase (cysE) Gene from the Wild-type and a Cysteine-excreting Mutant %D 1987 %J Microbiology, %V 133 %N 3 %P 515-525 %@ 1465-2080 %R https://doi.org/10.1099/00221287-133-3-515 %I Microbiology Society, %X SUMMARY: Serine acetyltransferase (SAT) from Escherichia coli is subject to feedback inhibition by l-cysteine. A mutant was isolated which excretes l-cysteine because of a lesion in cysE, the structural gene for SAT, rendering the enzyme less feedback sensitive. To analyse the structural basis for this mutation the cysE genes both from wild-type E. coli and the mutant strain were cloned and their nucleotide sequences determined. The cysE gene contained an open reading frame consisting of 819 bp, equivalent to a protein of 273 amino acids. The mutant gene showed a single base change in position 767 resulting in a methionine to isoleucine substitution. A causal connection between this SAT sequence alteration, feedback insensitivity and l-cysteine excretion was demonstrated. The SAT from the wild-type strain was purified. It was composed of a single polypeptide chain migrating in SDS gels according to an M r of 34000. As in Salmonella typhimurium, the enzyme was associated in a bifunctional complex with O-acetylserine (thiol)-lyase. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-133-3-515