Figure 1.

The σ⁷⁰ L402F substitution impairs λQ-mediated antitermination in vivo. (A) Presence of λQ allows RNAP that has initiated from P_R′ to read through transcription terminator t_R′. Blow-up depicts functionally important elements at P_R′, including the promoter −10 and −35 elements, the QBE, and the pause-inducing −10-like element. (B) Effect of substitution L402F in chromosomally encoded σ⁷⁰ on λQ-dependent lacZ expression from a P_R′-lacZ reporter in vivo. β-Galactosidase assays were performed to quantify lacZ expression levels in BN174 (WT) or ML9 (L402F) cells containing either a plasmid that directed the synthesis of λQ under the control of an IPTG-inducible promoter or a control plasmid that did not encode λQ. Note that the basal level of lacZ expression is ∼2-fold higher in ML9 cells. Inset shows ‘fold effect of λQ' values for cells grown in the presence of 100 μM IPTG; these values were determined by dividing the β-galactosidase activity in the presence of λQ by the β-galactosidase activity in the absence of λQ. Shown are the averages of three independent sets of measurements (and standard deviations).