TABLE 3.

Mutational analysis of the his leader region^a

Plasmid	Potential mRNA structure present upstream of lux AB genesb	Luciferase activities (lx/OD [103])		Strength of termination (fold)c	Antitermination factor (fold)d
		CDM+H	CDM−H
pJIM2530		960 ± 190	930 ± 160	1	1
pTer-4		23 ± 4	330 ± 40	42	14
pTer-3		10 ± 2	17 ± 0.6	96	1.7
pTer-2		5.2 ± 0.4	6.9 ± 0.3	185	1.3
pTer-4m1		10 ± 2	19 ± 3	96	1.9
pTer-4m2		12 ± 2	19 ± 3	80	1.6

^aTo study attenuation mechanism, the luciferase activity resulting from the insertion of various derivatives of the DNA segment carrying the his leader region between a constitutive promoter (P_orfD-repE) and the lux genes on a plasmid was measured in L. lactis growing in CDM with or without histidine. 

^bFusions are under the control of constitutive promoter P_orfD-repE from pJIM2530. 

^cQuotient of the lux value of the control plasmid pJIM2530 and that of the indicated plasmid in the presence of histidine. 

^dQuotient of the lux value obtained in the absence of histidine and that obtained in the presence of histidine for the same plasmid.