Hughes M.A. & Williams P.A. (2001) Cloning
and characterization of the pnb genes encoding the enzymes for 4-nitrobenzoate
catabolism in Pseudomonas putida TW3. J.Bacteriol. 183:
1225-1232
ABSTRACT
Pseudomonas putida strain TW3 is
able to metabolize 4-nitrotoluene via 4-nitrobenzoate (4NBen) and 3,4-dihydroxybenzoic
acid (protocatechuate, PCA) to central metabolites. We have cloned, sequenced
and characterized a 6 kbp fragment of TW3 DNA which contains five genes,
two of which encode the enzymes involved in the catabolism of 4NBen to
PCA. In order, they encode a 4NBen reductase (PnbA) which is responsible
for catalyzing the direct reduction of 4NBen to 4-hydroxylaminobenzoate
with the oxidation of 2 moles of NADH per mole of 4NBen, a reductase-like
enzyme (Orf1) which appears to have no function in the pathway, a regulator
protein (PnbR) of the LysR-family, a 4-hydroxylaminobenzoate lyase (PnbB)
which catalyzes the conversion of 4-hydroxylaminobenzoate to PCA and ammonium,
and a second lyase-like enzyme (Orf2) which is closely associated with
pnbB
but appears to have no function in the pathway. The central
pnbR
gene is transcribed in the opposite direction to the other four genes.
These genes complete the characterization of the whole pathway of 4-nitrotoluene
catabolism to the ring cleavage substrate PCA in P. putida strain
TW3.