Table II. Protein expression in the mutant strain CSR603C.

Plasmids	Constructions	Gene expression	Stop codon effect
		(3A′ + 2A′′)/2A′	(UAA/UGA)
pHN52	SD+-AUG-2A′-CCAUAA A	2.7 ± 0.3
pHN53	SD+-AUG-2A′-CCAUGA A	0.3 ± 0.02	pHN52/pHN53	9
pHN55	SD+-AUG-2A′-AGCUAA U	3.1 ± 0.4
pHN56	SD+-AUG-2A′-AGCUGA U	2.5 ± 0.4	pHN55/pHN56	1.2

CSR 603C is a mutant strain in which chromosomal DNA is inactivated and the plasmid test gene is overexpressed by UV irradiation. The initiation and termination codons are separated by a 2A′ gene sequence, as indicated. The SD preceding the AUG initiation codon is the SD⁺ variant, as shown in Figure 3. Cells were grown in M9 minimal medium without the inducer IPTG. The 3A′ values are normalized to 2A′ obtained by correction for the molecular weight of the A′ proteins (Björnsson et al., 1998). All contexts have GAC as the –2 codon (Figure 3). All data are based on at least four independent experiments.