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J. Bacteriol., Dec 1997, 7679-7686, Vol 179, No. 24
R Peist, A Koch, P Bolek, S Sewitz, T Kolbus and W Boos
malQ mutants of Escherichia coli lacking amylomaltase cannot grow on
maltose. They express the maltose system constitutively and are sensitive
to maltose when grown on another carbon source. In an attempt to isolate a
multicopy suppressor that would result in growth on maltose, we transformed
a malQ mutant with a gene bank of E. coli DNA which had been digested with
Sau3a and cloned in pBR322. We screened the transformants on MacConkey
maltose plates. A colony was isolated that appeared to be resistant to
maltose and was pink on these plates, but it was still unable to grow on
minimal medium with maltose as the carbon source. The plasmid was isolated,
and the gene causing this phenotype was characterized. The deduced amino
acid sequence of the encoded protein shows homology to that of lipases and
esterases. We termed the gene aes, for acetyl esterase. Extracts of cells
harboring plasmid-encoded aes under its own promoter exhibit a fivefold
higher capacity to hydrolyze p-nitrophenyl acetate than do extracts of
cells of plasmid-free strains. Similarly, strains harboring plasmid-encoded
aes are able to grow on triacetyl glycerol (triacetin) whereas the
plasmid-free strains are not. The expression of plasmid-encoded aes
resulted in strong repression of the maltose transport genes in malT+
strains (10-fold reduction), but not in a malT(Con) strain which is
independent of the inducer. Also, overproduction of MalT counteracted the
Aes-dependent repression, indicating a direct interaction between MalT and
Aes.
Copyright © 1997, American Society for Microbiology
Characterization of the aes gene of Escherichia coli encoding an enzyme with esterase activity
Department of Biology, University of Konstanz, Germany.
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