Regulation of Bacillus subtilis glutamate synthase genes by the nitrogen source.

The wild-type alleles of the gltA292 and gltB1 mutations of Bacillus subtilis have been identified in banks of B. subtilis DNA cloned in phage lambda. These mutations are thought to define the genes for the two subunits of glutamate synthase. Sequences having transforming activity for each allele were subcloned in plasmids and used as hybridization probes for measurements of the rates of synthesis and steady-state levels of glt mRNAs under different growth conditions. For both gltA and gltB, the level of mRNA varied according to the nitrogen source in the growth medium, to an extent sufficient to explain the variation in glutamate synthase activity under the same conditions. Two start points for mRNA synthesis were detected within the cloned DNA, one of which corresponded to the gltA locus. The other start point appears to define a transcription unit, separate from gltA and gltB, within which mutations cause loss of glutamate synthase activity.