TABLE 3.

Introducing a UAG stop codon at position 23 or 24 prevents induction^a

Strain	tnaC codons	β-Gal activity (Miller units)		Ratiob
		−Trp	+Trp
SVS1144 (wild type)	AUG..UGG12..CGC23CCU24UGA...	570 ± 15	18,920 ± 365	33
VK800	UAG	140 ± 18	2,100 ± 335	15
VK2900	UAG24	240 ± 25	280 ± 30
VK2900/pMY228	su UAGc	145 ± 14	160 ± 19
VK2800	UAG23	930 ± 36	850 ± 60
VK2800/pMY228	su UAGc	540 ± 100	2,350 ± 279	4

^aCultures were grown as for Table 2. More than five cultures of each type were assayed in each case. The nucleotide changes introduced are underlined. 

^bRatio of activities for cultures grown with Trp and without Trp. 

^csu UAG, a tryptophan-inserting UAG suppressor.