Table 2. In vivo activities of pmelAB::lac fusions in pRW50 in E.coli strains WAM131 (ΔlacU169) and WAM132 (ΔlacU169 ΔmelR).

Plasmid	β-Galactosidase activity of KK43 [Miller units (29)]
	WAM132 (ΔmelR host)			WAM131 (melR+ host)
	–melibiose	+melibiose	Fold induction	–melibiose	+melibiose	Fold induction
pAA121	4	1.8	0.5	2.7	188	70
pJW15	9	1581	175	30	1431	47
pCM118–314	6	1377	229	6	1367	227
pCM118–173	2.5	2.8	1.0	3	2	0.7

β-Galactosidase levels in two strains of E.coli containing pmelAB::lac fusions in pRW50 are shown. The promoter fragment used was KK43 containing sites 1′, 1, 2 and 2′. Cells were grown ± melibiose Cells also contained multicopy plasmids expressing full-length MelR (pJW15, pCM118–314), N-terminally truncated MelR173 (pCM118–173) or a control (pAA121). Assays were performed as in Webster et al. (1). Assays vary by <10% when repeated independently.