FIG. 4.

Transcription of the rrnB-lac and rrnB-Δ72-lac hybrid promoters in vivo and in vitro. (A) Activation by FIS in vivo; residues −88 to −38 are from rrnBp₁. Residues −37 to +59 are from lac and include the lac operator. Wild-type or mutant (Δ72) FIS site I (striped rectangle), the UP element (open rectangle), the −10 and −35 hexamers (filled squares), lac operator (stippled rectangle), and the transcription start site are indicated. β-Galactosidase activities at the right are from lysogens carrying the hybrid promoter-lacZ fusions (RLG1816, RLG1817, RLG1823, and RLG1824). (B) Activation by FIS in vitro. Supercoiled plasmids (pRLG1819 and pRLG1820) carrying the hybrid promoters pictured in panel A were transcribed in vitro in the presence of the indicated concentrations of purified FIS. Transcripts (about 220 nucleotides in length) from the hybrid promoter (containing the wild-type or mutant [Δ72] FIS site) and the RNA I promoter are indicated.