Table 1. Expression of lysC-lacZ transcriptional fusions.

	β-galactosidase activity*
Fusion	Low lysine	High lysine	Induction ratio†
WT	180	4.3	42
Xba-1	410	360	1.1
Xba-2	310	180	1.7
Xba-3	49	74	0.66

^*Fusions were integrated in single copy in strain BR151 (lys-3 metB10 trpC2). Cells were grown in Spizizen minimal medium (23) in the presence of lysine, then were split and grown in the presence of high lysine (50 μg/ml) or low lysine (5 μg/ml). Cells were harvested and assayed for β-galactosidase activity, expressed in Miller units (24). Maximal induction was observed 3 h after incubation in medium with low lysine.

^†Induction ratio is the ratio of activity under inducing conditions (low lysine) to the activity under repressing conditions (high lysine).