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J. Bacteriol., Dec 1996, 6790-6795, Vol 178, No. 23
B Nobelmann and JW Lengeler
In enteric bacteria, the hexitol galactitol (Gat) (formerly dulcitol) is
taken up through enzyme II (II(Gat)) of the phosphoenolpyruvate- dependent
phosphotransferase system (PTS), and accumulated as galactitol 1-phosphate
(Gat1P). The gat genes involved in galactitol metabolism have been isolated
from the wild-type isolate Escherichia coli EC3132 and cloned on a 7.8-kbp
PstI DNA fragment. They comprise six complete open reading frames and one
truncated open reading frame in the order gatYZABCDR'. The genes gatABC
code for the proteins GatA (150 residues) and GatB (94 residues), which
correspond to the hydrophilic domains IIA(Gat) and IIB(Gat), and GatC,
which represents a membrane-bound transporter domain IIC(Gat) (35 kDa, 427
residues). The three polypeptides together constitute a II(Gat) of average
size (671 residues). Gene gatD codes for a Gat1P-specific NAD-dependent
dehydrogenase (38 kDa, 346 residues), gatZ codes for a protein (42 kDa, 378
residues) of unknown function, and gatY (31 kDa, 286 residues) codes for a
D-tagatose-1,6-bisphosphate aldolase with similarity to other known
ketose-bisphosphate aldolases. The truncated gatR' gene, whose product
shows similarity to the glucitol repressor GutR, closely resembles a gatR
gene fragment from E. coli K-12. The gat genes map in both organisms at
similar positions, in E. coli K-12, where they are transcribed
counterclockwise at precisely 46.7 min or 2,173 to 2,180 kbp. The genes are
expressed constitutively in both strains, probably due to a mutation(s) in
gatR. Transcription initiation sites for the gatYp and the gatRp promoters
were determined by primer extension analysis.
Copyright © 1996, American Society for Microbiology
Molecular analysis of the gat genes from Escherichia coli and of their roles in galactitol transport and metabolism
Universitat Osnabruck, Fachbereich Biologie/Chemie, Federal Republic of Germany.
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