TABLE 4.

Effect of a tnrA mutation on GltR24-dependent gltA expression^a

Strain	Genotype	β-Galactosidase activity, Miller units (gltA-lacZ fusion)
		Ammonium	Ammonium + proline	Proline
LG200	Wild type	75.8	50.4	<0.6
LG200-S	gltC	NGb	0.9	0.2
BB614	gltR24 gltC	34.2	12.5	1.6
BB873	gltR24 gltC tnrA	32.0	NDc	24.3

^aThe various strains, all carrying a gltAp⁺-lacZ fusion, were grown to mid-exponential phase in the indicated glucose minimal medium and assayed for β-galactosidase activity. 

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

^cND, not determined.