Table 2. Effect of excess Mlc or NagC on expression of nagE–lacZ fusions.

		Control (pTZ19)	PTZ(Mlc)		pTZ(NagC)
		Units	Units	Rep	Units	Rep
nagBE–lacZ	looped	1410	25	56	16	88
nagE–lacZ	single site	1120	40	28	420	2.7
nagE–lacZ s.o.	single site with super-operator	325	42	8	3.3	98

IBPC529C (nagC, mlc-1) was lysogenised with the three nagE–lacZ fusions and then transformed with plasmids overexpressing Mlc or NagC from the lac promoter in a pTZ vector or the empty vector plasmid (pTZ19, control) as indicated. IBPC529C is Δlac so that expression from the lac promoter of the pTZ plasmids expressing Mlc and NagC is constitutive. Bacteria were grown in MOPS medium with 0.4% glycerol, 0.5% cas amino acids and 0.5 mg/ml ampicillin. β-galactosidase activities were measured throughout the exponential growth phase and the values are the mean of two independent cultures. Rep (repression) is the relative decrease in expression of the fusion caused by the presence of the NagC or Mlc plasmid compared with the empty vector plasmid.