TABLE 1.

Effect of nmrA deletions on nitrogen metabolite repression of amdS::lacZ expression

Nitrogen sourcea	β-Galactosidase level (Miller units/min/mg of protein)b
	nmrA	% Dere- pressionc	ΔnmrA::bleoR	% Dere- pressionc
Ala	12.2 ± 1.3		13.7 ± 1.5
NH4	1.8 ± 0.4	15	4.6 ± 1.5	34
Gln	2.4 ± 0.2	20	6.3 ± 0.8	46
Ala + GABA	91.2 ± 7.3		147.4 ± 16.0
Ala + GABA + NH4	6.6 ± 1.5	7	48.2 ± 10.1	33

^aMycelium was grown for 16 h at 37°C in glucose minimal medium (9) containing in each case the following nitrogen sources: 10 mM l-alanine (Ala), 10 mM ammonium tartrate (NH₄), 10 mM l-glutamine (Gln), and 10 mM γ-amino-butyric acid (GABA). 

^bβ-Galactosidase levels encoded by an amdS::lacZ translational fusion gene integrated by gene replacement at the amdS locus were assayed by the method of Davis et al. (11) and are expressed as means ± standard errors. 

^cThe percentage of derepression is calculated as the level of enzyme activity under repressed conditions relative to that under nonrepressed conditions: NH₄ and Gln relative to the limiting nitrogen source Ala, Ala plus GABA plus NH₄ relative to Ala plus GABA.