f 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
- Authors: DAGMAR DENK, AUGUST BÖCK
- First Published Online: 01 March 1987, Microbiology 133: 515-525, doi: 10.1099/00221287-133-3-515
- Subject: Genetics And Molecular Biology
- Issue Published:
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.
© Societ for General Microbiology 1987 | Published by the Microbiology Society
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