TABLE 1.

thi promoter region from bacimethrin-resistant mutants directs increased expression^a

Plasmid	β-Galactosidase activityb ± SD		Fold repression
	Without thiamine	With thiamine
pThi	2,402 ± 219	756 ± 31	3.2
pThi4	8,947 ± 1,303	1,685 ± 353	5.3
pThi8	8,933 ± 1,825	2,036 ± 515	4.4

^aDerivatives of LT2 containing the indicated plasmid were grown overnight in minimal medium containing chloramphenicol and subcultured into minimal medium with or without thiamine. Subcultures were grown to 0.3 to 0.4 A₆₅₀ before being assayed. β-Galactosidase activity was assayed as previously described (9, 24), except that volumes were reduced 10-fold, and absorbance was read in a microtiter plate by a Spectramax Plus (Molecular Devices). 

^bActivities are reported as nanomoles of o-nitrophenyl-β-d-galactopyranosidase hydrolyzed/minute/A₆₅₀ ± 1 standard deviation of the mean.