TABLE 2.

β-Galactosidase levels of E. coli strains with plasmids containing tnaC of P. vulgaris or tnaC of E. coli, followed by a corresponding tnaA-lacZ gene fusion^a

tnaC source	tnaC change	β-Galactosidase activity (Miller units)b		Induction ratio (+1MTrp/ −1MTrp)
		−1MTrp	+1MTrp
Proteus vulgaris	wt	300 ± 70	2,300 ± 76	8
	K33R	320 ± 66	2,500 ± 66	8
	K33I	340 ± 73	3,000 ± 54	9
	K33R-K34R	310 ± 56	2,450 ± 86	8
	K33I-K34I	340 ± 60	3,400 ± 65	10
	ΔK33-34	550 ± 80	7,000 ± 75	13
	TAA35TGA	320 ± 76	2,500 ± 66	8
	W20R	90 ± 26	110 ± 76	1
	D24A	100 ± 26	200 ± 20	2
	L27A	110 ± 26	670 ± 23	6
	P32A	200 ± 26	250 ± 26	1
Escherichia coli	wt	300 ± 760	12,300 ± 106	41
	W12R	120 ± 36	110 ± 26	1
	D16A	150 ± 30	200 ± 20	1
	P24A	110 ± 32	170 ± 23	1

^aCultures of the E. coli W3110 strain containing the pAVK9 (tnaC of Proteus vulgaris) or pPDG100 (tnaC of E. coli) plasmid or its variants were grown in minimal medium plus 0.2% glycerol and 0.05% acid hydrolyzed casein, with (+1MTrp) or without (−1MTrp) 100 μg/ml dl-1-methyl-tryptophan, at 37°C. wt, wild type.

^bβ-Galactosidase assays (see Materials and Methods) were performed on samples obtained from three independent experiments.