Mj. Hussein et al., CHARACTERIZATION OF MUTATIONS THAT ALLOW P-AMINOBENZOYL-GLUTAMATE UTILIZATION BY ESCHERICHIA-COLI, Journal of bacteriology (Print), 180(23), 1998, pp. 6260-6268
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.