ISOLATION AND PROPERTIES OF ESCHERICHIA-COLI-K-12 MUTANTS IMPAIRED IN THE UTILIZATION OF GAMMA-AMINOBUTYRATE

Mutants of E. coli K-12 CS101B were isolated that have lost the ability to utilize .gamma.-aminobutyrate as a N source. One class of mutants, which were not affected in the utilization of other N sources (proline, arginine, glycine), included many isolates with lesions in .gamma.-aminobutyrate transport or in its transamination and 1 mutant completely devoid of succinic semialdehyde dehydrogenase [EC 1.2.1.16] activity and exhibiting low .gamma.-aminobutyrate transport and transamination. .gamma.-Aminobutyrate-utilizing revertants of the latter recovered full transport and transamination capacities but remained dehydrogenaseless. Another class of mutants showed pleiotropic defects in N metabolism. One such mutant was lacking glutamate synthase activity. The genes specifying the synthesis of .gamma.-aminobutyrate permease, gabP, .gamma.-aminobutyrate transaminase, gabT and succinic semialdehyde dehydrogenase, gabD, and the control gene, gabC, that coordinately regulates their expression all form a cluster on the E. coli chromosome, linked to the srl and recA loci (at 57.5 min). The mutations with pleiotropic effects on the metabolism of nitrogenous compounds are not linked to the gab cluster.