Table 2.

Rate of read-through at nonsense mutations in lacZ

Strain/lacZ	Relative β-galactosidase activity*
	GGA	UAG	UAA	UGA	Δ
hemK+	100  ± 3.7	0.35  ± 0.087	0.59  ± 0.10	0.65  ± 0.048	0.25  ± 0.091
ΔhemK	100  ± 1.5	1.5  ± 0.24	0.33  ± 0.0065	1.5  ± 0.10	0.12  ± 0.015

CA293 (hemK⁺) or CK783 (ΔhemK) was transformed with a set of pKK232-Z derivatives, in which GGA, UAG, UAA, or UGA was the seventh lacZ codon (shown in the lacZ row) or in which the segment from the 5′ nontranslated region to the seventh codon of lacZ was deleted (Δ, shown in the lacZ row), and grown on LB broth to 0.6–0.7 OD₆₀₀. The β-galactosidase activity of the cells was assayed as described (13). 

^*The average ± SD (of three experiments) β-galactosidase activity (Miller units) of each lacZ derivative is shown as the percentage of that of the reference gene (GGA) in the same strain.