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This repressor binds to or1 and or2 cooperatively but

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Unformatted text preview: enough repressor to bind to the early operators and prevent further early RNA synthesis • The promoter used for establishment of lysogeny is PRE, which lies to the right of PR and cro. Transcription from this promoter goes leftward through the cI gene. The products of the delayed early genes CII and CIII also participate in this process: CII, by directly stimulating polymerase to binding to PRE and PI; CIII, by slowing degradation of CII. Summary 3 • The promoter that is used to maintain lysogeny is PRM. It comes into play after transcription from PRE makes possible the burst of repressor synthesis that establishes lysogeny. This repressor binds to OR1 and OR2 cooperatively, but leaves OR3 open. • RNAP binds to PRM, which overlaps OR3 in such a way that it contacts the repressor bound to OR2. This protein-protein interaction is required for this promoter to work efficiently. • High levels of repressor can repress transcription from PRM via DNA looping when repressor dimers are bound to OR1, OR2, and OR3 Summary 4 • Whether a given cell is lytically or lysogenically infected by phage λ depends on the outcome of a race between the products of the cI and cro genes. • The cI gene codes...
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