TABLE 1.

Regulation of the expression of a levD′-′lacZ fusion by CcpA, P-Ser–HPr, and P-Ser–Crh

Straina	Relevant genotype	β-Galactosidase activity (U/mg of protein)b in:		Repression factor
		CSK Fru	CSK Fru Glu
QB5081	crh+ ptsH+	220	17	13
QB5224	ptsH1	405	87	4.5
QB7158	crh1	270	27	10
QB7159	ptsH1 crh1	390	220	1.5
QB7160	hprK::aphA3	370	282	1.3

^aAll strains contain a levD′-′lacZ translational fusion integrated in the amyE gene and a trpC2 mutation. 

^bSpecific activities of β-galactosidase were determined in extracts prepared from exponentially growing cells (absorbance at 600 nm, 0.7 to 1). The mean values of at least three independent experiments are presented. Cells were grown in CSK medium, which is C minimal medium supplemented with potassium succinate (6 g/liter) and potassium glutamate (8 g/liter) (17), or on CSK medium containing 0.2% fructose or 0.2% fructose plus 1% glucose. The method of Miller was used for the determination of β-galactosidase activity (21).