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Figure 1
The effect of gp33 on T4 late open promoter complexes. (A) Open promoter complexes monitored by KMnO4 probing. RNAP was combined with gp33, where indicated (Step 1), followed by the addition of P23 promoter DNA, 32P-labeled on the transcribed (template) strand and incubation for 5 or 20 min, as specified. Alternatively, gp33 was added to preformed open promoter complexes (Step 2). DNA cleavage at T +2, -6, and -8, indicative of promoter opening, is shown by asterisks. (B) Open complexes monitored by DNase I footprinting. Complexes containing the indicated RNAP were formed for 20 min, with gp33 added before DNA (Step 1) or after open complex formation (Step 2), as indicated. Heparin was added (to 100  g/ml) for 30 s prior to DNase addition. Lanes A: A-sequence ladders; lanes 1: DNA without protein. The DNA segment protected by the open promoter complex is indicated by the vertical bar, with gp33-dependent changes highlighted by striping.
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