TABLE 4.

Specific activity of β-galactosidase in lrp⁺ and lrp strains having leuP-lacZ transcriptional fusions at the λ attachment site^a

Strain	lrp allele	leu attenuatorb	Sp. act. of β-galactosidasec in medium		Ratio of sp. act. (without Leu/with Leu)
			Without Leu	With Leu
CV1520	lrp+	Absent	1,870 ± 425	2,780 ± 243	0.67
CV1521	lrp-35::Tn10	Absent	2,020 ± 240	1,960 ± 293	1.0
CV1517	lrp+	Present	432 ± 110	80.7 ± 10.4	5.5
CV1518	lrp-35::Tn10	Present	1,950 ± 518	64.0 ± 8.9	30

^aCulture conditions as in legend to Table 3. 

^bStrains CV1520 and CV1521 have region −247 to +18 from the leu operon (contains leu promoter but not attenuator) attached to a lacZ gene on phage λ in single copy at the λ attachment site (Fig. 1). Strains CV1517 and CV1518 are similar except that they have region −247 to +230 from the leu operon which contains both the leu promoter and attenuator. 

^cSpecific activity in Miller units. Values represent the means and standard deviations for multiple samples taken throughout the log growth phase from at least two independent experiments.