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J. Bacteriol., 09 1995, 4857-4864, Vol 177, No. 17
JK Rosentel, F Healy, JA Maupin-Furlow, JH Lee and KT Shanmugam
Escherichia coli mutants with defined mutations in specific mod genes that
affect molybdate transport were isolated and analyzed for the effects of
particular mutations on the regulation of the mod operon as well as the
fdhF and hyc operons which code for the components of the formate
hydrogenlyase (FHL) complex. phi (hyc'-'lacZ+) mod double mutants produced
beta-galactosidase activity only when they were cultured in medium
supplemented with molybdate. This requirement was specific for molybdate
and was independent of the moa, mob, and moe gene products needed for
molybdopterin guanine dinucleotide (MGD) synthesis, as well as Mog protein.
The concentration of molybdate required for FHL production by mod mutants
was dependent on medium composition. In low-sulfur medium, the amount of
molybdate needed by mod mutants for the production of half-maximal FHL
activity was increased approximately 20 times by the addition of 40 mM of
sulfate, mod mutants growing in low-sulfur medium transported molybdate
through the sulfate transport system, as seen by the requirement of the
cysA gene product for this transport. In wild-type E. coli, the mod operon
is expressed at very low levels, and a mod+ merodiploid E. coli carrying a
modA-lacZ fusion produced less than 20 units of beta- galactosidase
activity. This level was increased by over 175 times by a mutation in the
modA, modB, or modC gene. The addition of molybdate to the growth medium of
a mod mutant lowered phi (modA'-'lacZ+) expression. Repression of the mod
operon was sensitive to molybdate but was insensitive to mutations in the
MGD synthetic pathway.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
Molybdate and regulation of mod (molybdate transport), fdhF, and hyc (formate hydrogenlyase) operons in Escherichia coli
Department of Microbiology and Cell Science, University of Florida, Gainesville 32611, USA.
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