TABLE 3.

β-Galactosidase activity from the hpx operon fusions in the genetic background of strain KC2653 grown under different conditions of nitrogen availability

Promoter fusion	β-Galactosidase sp act (U/mg) from cells grown ina:
	GNGln	GNGlnHx	GNGlnUr	GGln	GGlnHx	GGlnUr	GHx	GUr
Φ(hpxD-lacZ)	11	18	8.0	589	23,609	463	33,184	1,447
Φ(hpxR-lacZ)	132	125	117	149	118	149	138	136
Φ(hpxO-lacZ)	624	579	489	820	729	706	999	916
Φ(hpxP-lacZ)	44	42	47	348	1,944	1,109	4,170	3,892

^aActivity values are the averages from four assays with a standard error of 15% or less. One unit of β-galactosidase activity corresponds to the amount of enzyme that hydrolyzes 1 nmol of ONPG per min. Growth media were as follows: GNGln, nitrogen-excess medium, containing 0.4% glucose and 0.2% each ammonium sulfate and l-glutamine; GNGlnHx and GNGlnUr, same as GNGln but containing 0.1% hypoxanthine or 0.1% uric acid, respectively; GGln, nitrogen-limiting medium, containing 0.4% glucose and 0.04% l-glutamine; GGlnHx and GGlnUr, same as GGln but containing 0.1% hypoxanthine or 0.1% uric acid, respectively; GHx and GUr, 0.4% glucose minimal media containing, respectively, 0.1% hypoxanthine or 0.1% uric acid as the sole nitrogen source.