Table 4.

Effect of Rho termination factor on trp operon expression

StrainRelevant genotypeaTranslational fusionUAA stop codon in trpEb β-Gal activitycβ-Gal ratio (−Trp/+Trp)
−Trp+Trp
PLBS127WTtrpL trpE′-′lacZ NAd 26 ± 50.2 ± 0.03130
PLBS289WT trpL rho::neo trpE′-′lacZ NA 39 ± 70.6 ± 0.0365
PLBS142WTtrpL trpED′-′lacZ No190 ± 202.1 ± 0.590
PLBS138WTtrpL trpED′-′lacZ Yes24 ± 60.5 ± 0.148
PLBS143WT trpL sup-3 trpED′-′lacZ No240 ± 502.9 ± 0.583
PLBS139WT trpL sup-3 trpED′-′lacZ Yes80 ± 81.0 ± 0.280
PLBS293WT trpL rho::neo trpED′-′lacZ No210 ± 1414 ± 115
PLBS291WT trpL rho::neo trpED′-′lacZ Yes27 ± 312 ± 22
PLBS294WT trpL rho::neo sup-3 trpED′-′lacZ No316 ± 2021 ± 215
PLBS292WT trpL rho::neo sup-3 trpED′-′lacZ Yes114 ± 1014 ± 28
  • a WT trp leader (WTtrpL). UAA stop codons are recognized by the tRNA suppressor encoded by the sup-3 allele. rho is disrupted by a neo insertion.

  • b Presence (Yes) or absence (No) of the engineered stop codon within the coding sequence of trpE.

  • c β-Galactosidase (β-Gal) activity expressed from the trpE′-′lacZ and thetrpED′-′lacZ fusions is given in Miller units (21). Cells were grown in the absence (−Trp) or presence (+Trp) of tryptophan (200 μM). The values are averages from at least four independent experiments ± standard deviation.

  • d NA, not applicable.