TABLE 4.

Effect of pH on the expression of invasion-defective TnphoA gene fusions

Bacterial straina	Locus/amino acid position	Mean PhoA activity (Miller units)b ± SEM		Ratioc
		LB, pH 5.0	LB, pH 6.5
A1	Z::TnphoA	662 ± 229	187 ± 34	0.3
K14	invG/53	22 ± 11	497 ± 98	22.5
H5	prgH/184	171 ± 70	1,027 ± 145	6.0
I25	cpxA/89	165 ± 23	128 ± 4	0.8
L5	damX/222	120 ± 39	125 ± 10	1.0

^aStrains were grown to mid-logarithmic phase (OD₆₀₀ of ≈0.6) in LB buffered with 0.1 M MES at pH 5.0 or 6.5 with kanamycin and tetracycline. Cell extracts were prepared by sonication, and the amount (milligrams) of protein was determined by the Bio-Rad assay. 

^bAlkaline phosphatase activity was measured as described in Materials and Methods. The data represent means of duplicate samples from four independent experiments. 

^cRatio of PhoA activity LB at pH 6.5/LB at pH 5.0.