TABLE 2.

Basal and induced expression in strains with constructs containing one of three stop codons (at 37°C)

Strain	Relevant features	Avg β-Gal activity (Miller units) ± SDb
		−Trp	+Trp	+Trp/ −Trpc
SVS1144	tnaC-UGA-tnaA′-′lacZ	518 ± 20	14,019 ± 1,159	27
VK800	tnaC-UAG-tnaA′-′lacZ	99 ± 12	1,919 ± 252	19
VK800/ pMY228a	VK800 with su UAG (Trp)	367 ± 33	1,199 ± 82	3
PDG1158	tnaC-UAA-tnaA′-′lacZ	223 ± 17	8,344 ± 940	37
PDG1184	tnaC stop to UUAd	239 ± 9	2,076 ± 97	9

^apMY228, a plasmid carrying a Trp-inserting tRNA^Trp UAG suppressor 

^bCultures were grown at 37°C in minimal medium (49) plus 0.2% glycerol and 0.05% acid-hydrolyzed casein, with (+Trp) or without (−Trp) 100 μg of l-Trp per ml. For β-Gal assay conditions, see Materials and Methods. Values are for at least five cultures of each type. 

^cRatio of β-Gal activities with and without Trp. 

^dAdds five sense codons to tnaC to a UAG.