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J. Bacteriol., 06 1996, 3260-3269, Vol 178, No. 11
S Tong, A Porco, T Isturiz and T Conway
Three genes involved in gluconate metabolism, gntR, gntK, and gntU, which
code for a regulatory protein, a gluconate kinase, and a gluconate
transporter, respectively, were cloned from Escherichia coli K-12 on the
basis of their known locations on the genomic restriction map. The gene
order is gntU, gntK, and gntR, which are immediately adjacent to asd at
77.0 min, and all three genes are transcribed in the counterclockwise
direction. The gntR product is 331 amino acids long, with a
helix-turn-helix motif typical of a regulatory protein. The gntK gene
encodes a 175-amino-acid polypeptide that has an ATP-binding motif similar
to those found in other sugar kinases. While GntK does not show significant
sequence similarity to any known sugar kinases, it is 45% identical to a
second putative gluconate kinase from E. coli,gntV. The 445-amino-acid
sequence encoded by gntU has a secondary structure typical of
membrane-spanning transport proteins and is 37% identical to the gntP
product from Bacillus subtilis. Kinetic analysis of GntU indicates an
apparent Km for gluconate of 212 microM, indicating that this is a
low-affinity transporter. Studies demonstrate that the gntR gene is
monocistronic, while the gntU and gntK genes, which are separated by only 3
bp, form an operon. Expression of gntR is essentially constitutive, while
expression of gntKU is induced by gluconate and is subject to fourfold
glucose catabolite repression. These results confirm that gntK and gntU,
together with another gluconate transport gene, gntT, constitute the GntI
system for gluconate utilization, under control of the gntR gene product,
which is also responsible for induction of the edd and eda genes of the
Entner- Doudoroff pathway.
Copyright © 1996, American Society for Microbiology
Cloning and molecular genetic characterization of the Escherichia coli gntR, gntK, and gntU genes of GntI, the main system for gluconate metabolism
Department of Food Science and Technology, University of Nebraska- Lincoln, 68588-0919, USA.
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