CLONING AND SEQUENCING SHOW THAT 4-HYDROXYBENZOATE HYDROXYLASE (POBA)IS REQUIRED FOR UPTAKE OF 4-HYDROXYBENZOATE IN RHIZOBIUM-LEGUMINOSARUM

Mutants of Rhizobium leguminosarum bv. viciae MNF300 and R. leguminosa rum bv. trifolii WU95 unable to accumulate 4-hydroxybenzoate lack 4-hy droxybenzoate hydroxylase. The capacity of these mutants to take up an d grow on 4-hydroxybenzoate was restored by a 2.0 kb EcoRI-PstI DNA fr agment. This contained only one ORF which had over 60% DNA sequence si milarity with the structural gene for 4-hydroxybenzoate hydroxylase (p obA) from Pseudomonas spp. and Acinetobacter. Reported effects of meta bolic inhibitors and substrate analogues on the apparent uptake of 4-h ydroxybenzoate have now been shown to be due to their direct effect on 4-hydroxybenzoate hydroxylase. We propose that uptake of 4-hydroxyben zoate is via a metabolic 'drag' mechanism dependent on the activity of the pobA gene product.