Table 2.

The β′ subunit of RNAP titrates BglG in vivo

Plasmid	Plasmid-encoded RNAP subunit	Phenotype on MacConkey–lactose plates*	β-gal activity†, units
			−IPTG	+IPTG
pLAX185	α	red	156	105
pMKSe2	β	red	153	102
pMKA201	β′	white	102	8
pBR322	—	red	138	ND

The experiment was carried out in MA200-1 which carries a bgl-lacZ transcriptional fusion and expresses bglG constitutively because of a mutation in bglF (33). 

^*IPTG was added to a final concentration of 0.5 mM to plates and 1 mM to liquid medium. 

^†The values represent the average of four independent measurements. IPTG, isopropyl β-d-thiogalactoside. ND, not determined.