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J. Bacteriol., 12 1996, 7099-7105, Vol 178, No. 24
KE Baker, KP Ditullio, J Neuhard and RA Kelln
Mutants deficient in orotate utilization (initially termed out mutants)
were isolated by selection for resistance to 5-fluoroorotate (FOA), and the
mutations of 12 independently obtained isolates were found to map at 79 to
80 min on the Salmonella typhimurium chromosome. A gene complementing the
mutations was cloned and sequenced and found to possess extensive sequence
identity to characterized genes for C4- dicarboxylate transport (dctA) in
Rhizobium species and to the sequence inferred to be the dctA gene of
Escherichia coli. The mutants were unable to utilize succinate, malate, or
fumarate as sole carbon source, an expected phenotype of dctA mutants, and
introduction of the cloned DNA resulted in restoration of both
C4-dicarboxylate and orotate utilization. Further, succinate was found to
compete with orotate for entry into the cell. The S. typhimurium dctA gene
encodes a highly hydrophobic polypeptide of 45.4 kDa, and the polypeptide
was found to be enriched in the membrane fraction of minicells harboring a
dctA+ plasmid. The DNA immediately upstream of the deduced -35 region
contains a putative cyclic AMP-cyclic AMP receptor protein complex binding
site, thus affording an explanation for the more effective utilization of
orotate with glycerol than with glucose as carbon source. The E. coli dctA
gene was cloned from a lambda vector and shown to complement
C4-dicarboxylate and orotate utilization in FOA-resistant mutants of both
E. coli and S. typhimurium. The accumulated results demonstrate that the
dctA gene product, in addition to transporting C4- dicarboxylates, mediates
the transport of orotate, a cyclic monocarboxylate.
Copyright © 1996, American Society for Microbiology
Utilization of orotate as a pyrimidine source by Salmonella typhimurium and Escherichia coli requires the dicarboxylate transport protein encoded by dctA
Department of Chemistry, University of Regina, Saskatchewan, Canada.
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