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Lysogeny maintenance weaver 2002 molecular biology ed

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Unformatted text preview: uce cloudy plaques because some cells have established lysogeny rather than dying • almost all mutant phage in lytic state means all host cells lysed by infection leading to clear plaques MAINTENANCE OF LYSOGENY MAINTENANCE Weaver 2002 Molecular Biology Ed. 2 λ repressor is transcribed from PRM - promoter “repressor maintenance” ∀ λ repressor protein produced by cI binds as dimer to OL cI & OR independently, preventing transcription from PL & PR promoters • positive autogenous circuit: λ repressor binding to OR positive The λ repressor monomer Various surfaces are involved in different activities carried out by the λ repressor. N indicates the amino domain, C the carboxyl domain. “Tetramerization” denotes the region where two dimers interact when binding cooperatively to adjacent sites on DNA (more later) Repressor bound at OR2 contacts RNAP at PRM, activating expression LYSOGENIC CELL IMMUNITY LYSOGENIC • cI repressor protein confers immunity to lysogenic cI bacterial cells from re-infection by other λ phage • When new phage DNA enters prophage-containing When bacterium, the new phage DNA immediately bound by λ repressor at OL & OR • Lytic cascade cannot be initiated • If transcription from PRM requires binding of λ repressor itself, then how is cI synthesis cI established in the first place? established • cI mRNA synthesis is first established from another promoter: PRE another ESTABLISHMENT OF LYSOGENY ESTABLISHMENT Weaver 2002 Molecular Biology Ed. 2 • • • • if transcription from PRM requires binding of repressor itself, how if is λ repressor synthesis established in the first place? is when λ DNA enters new host, immediate early & then delayed early when genes expressed - among products of delayed early genes are CII & CIII proteins CIII between cro & cII genes is “repressor establishment” promoter PRE between cro cII cI repressor gene transcribed from PRE but PRE does not have conserved -10 and -35 core --> RNAP recognizes PRE if bound by CII protein protein RNAP BINDS PRE ONLY WITH CII • Although –35 and –10 Although PRE regions not conserved relative to conventional bacterial operons, they are bound by RNAP as shown by both footprinting and mutational analysis mutational ESTABLISHMENT OF LYSOGENY ESTABLISHMENT • conventional DNase I conventional footprinting reveals that CII binds PRE between –21 & –44 (around –35 regi...
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