CHARACTERIZATION OF MUTATIONS THAT ALLOW P-AMINOBENZOYL-GLUTAMATE UTILIZATION BY ESCHERICHIA-COLI

An Escherichia coli strain deficient in p-aminobenzoate synthesis was mutagenized, and derivatives were selected for growth on folic acid. S upplementation was shown to be due to p-aminobenzoyl-glutamate present as a breakdown product in commercial folic acid preparations. Two cla sses of mutations characterized by the minimum concentration of p-amin obenzoyl-glutamate that could support growth were obtained. Both class es of mutations were genetically and physically mapped to about 30 min on the E. coli chromosome. A cloned wild-type gene from this region, abgT (formerly ydaH) could confer a similar p-aminobenzoyl-glutamate u tilization phenotype on the parental strain. Interruption of abgT on t he plasmid or on the chromosome of the mutant strain resulted in a los s of the phenotype, abgT was the third gene in an apparent operon cont aining abgA, abgB, abgT, and possibly ogt and might be regulated by a divergently transcribed LysR-type regulator encoded by abgR, Two diffe rent single-base-pair mutations that gave rise to the p-aminobenzoyl-g lutamate utilization phenotype lay in the abgR-abgA intercistronic reg ion and appeared to allow the expression of abgT. The second class of mutation was due to a tandem duplication of abgB and abgT fused to fnr , The abgA and abgB gene products were homologous to one another and t o a family of aminoacyl aminohydrolases. p-Aminobenzoyl-glutamate hydr olysis could be detected in extracts from several of the mutant strain s, but intact: abgA and abgB were not essential for p-aminobenzoyl-glu tamate utilization when abgT was supplied in trans.