TABLE 5.

Effect of a tnrA mutation on Box I- and Box II-independent gltA expression^a

Strain	Genotype	gltA regulatory regionb fused to lacZ	β-Galactosidase activity, Miller units (gltA-lacZ fusion)
			Ammonium	Ammonium + proline	Proline
LG700	Wild type	gltAp700	2.5	1.7	≤0.2
LG700-S	gltC	gltAp700	NGc	1.6	≤0.2
LG700-ST	gltC tnrA	gltAp700	NG	1.9	1.9
LG702	Wild type	gltAp702	1.9	1.6	≤0.2
LG702-S	gltC	gltAp702	NG	2.1	≤0.2
LG702-ST	gltC tnrA	gltAp702	NG	2.1	2.2

^aThe various strains were grown to mid-exponential phase in the indicated glucose minimal medium and assayed for β-galactosidase activity. 

^bThe gltAp700 promoter has Box I deleted and contains nucleotides from positions −56 to +119 with respect to the gltA transcription start point; the gltAp702 promoter had both Box I and Box II deleted and contains nucleotides from positions −45 to +119 (Fig. 1) (2). 

^cNG, no growth. gltC mutants are glutamate auxotrophs and therefore cannot grow with ammonium as the sole nitrogen source.