Fig. 3.

Antitermination of bgl operon transcription in vivo requires the general PTS proteins. Total RNA was prepared from 3 bgl⁺ E. coli strains, MA10 (wt), a Δpts derivative of MA10 (Δpts), and a version of the latter strain transformed with a pBR322-based plasmid encoding EI and HPr, which were grown with or without the β-glucoside salicin. The different RNA preparations were hybridized to a radioactively labeled, single-stranded bgl probe and analyzed by the S1 nuclease protection assay, as described in Materials and Methods. The samples were separated on a denaturing polyacrylamide-urea gel. T, terminated transcripts; AT, antiterminated transcripts; M, [γ-³²P]ATP-labeled, denatured, HinfI-cleaved ΦX174 DNA fragments; Cont, total RNA prepared from MA110, which is isogenic to MA10 but lacks the bgl operon, containing pBR322, and analyzed by the S1 nuclease protection assay. The ratio between the terminated and antiterminated transcripts in MA10 (wt), calculated as described in Fig. 2, in 7 independent experiments was 2.2 ± 0.8. The ratio between the 2 transcripts in the Δpts derivative of MA10 (Δpts) transformed with a plasmid encoding EI and HPr, calculated from 3 independent experiments, was 2.4 ± 0.3.