Table 3.

Effects of a prfA1 mutation on basal and induced expression in strains with one of three stop codons (at 30°C)

StrainRelevant featuresAvg β-Gal activity (Miller units) ± SDa
−Trp+Trp+Trp/ −Trpb
SVS1144tnaC-UGA-tnaA′-′lacZ729 ± 2416,244 ± 72922
VK1145SVS1144prfA1421 ± 526,833 ± 87516
VK800tnaC-UAG-tnaA′-′lacZ49 ± 31,102 ± 10422
VK801VK800prfA13,093 ± 2957,096 ± 5482.3
PDG1158tnaC-UAA-tnaA′-′lacZ163 ± 36,554 ± 35740
VK1159PDG1158prfA1459 ± 217,634 ± 86117
PDG1184tnaC stop to UUAc72 ± 4626 ± 809
VK1185PDG1184prfA1513 ± 23881 ± 451.7
  • a Cultures were grown at 30°C in minimal medium (49) plus 0.2% glycerol and 0.05% acid-hydrolyzed casein, with (+Trp) or without (−Trp) 100 μg ofl-Trp per ml. For β-Gal assay conditions, see Materials and Methods. Values are for at least five cultures of each type.

  • b Ratio of β-Gal activities with and without Trp.

  • c Adds five codons to tnaC to a UAG.