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Immediate early genes n cro are transcribed cro

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Unformatted text preview: ENY: synthesis established synthesis λ IMMEDIATE IMMEDIATE EARLY GENES • 1. When λ enters a host, the 1. immediate early genes N & cro are transcribed cro independently by host RNAP independently • N: antitermination factor acts N: at nut (Nutilization) sites & nut ilization) enables transcription to proceed into delayed early genes genes • cro: blocks lysogeny by (i) blocks preventing λ repressor synthesis synthesis λ REGULATORY REGION REGULATORY • 2 transcription units for immediate early genes, N and transcription cro, transcribed in opposite directions from promoters PL & PR • RNAP stops at Rho-dependent terminators tL1 & tR1 in RNAP L1 absence of the N gene product, pN N ANTITERMINATION • in absence of pN, RNAP in transcript terminates at tL1 and makes N mRNA only product makes • in presence of pN, RNAP can in read through tL1 & tR1 terminators into distal delayed early genes early – pN binds transcribed nut pN nut region and also to NusA protein complex; together the proteins alter RNAP so it reads through terminators reads Weaver 2002 Molecular Biology Ed. 2 λ DEVELOPMENT DEVELOPMENT Weaver 2002 Molecular Biology Ed. 2 • Immediate early genes: N and cro cro • Cro protein promotes the lytic cycle by Cro preventing cI repressor synthesis cI • Delayed early genes: expressed expressed because of pN - includes 2 replication, 7 recombination, and 3 regulatory genes with opposing functions genes (i) cII/cIII involved in λ repressor (i) cII synthesis synthesis (ii) Q, which encodes pQ (ii) which antitermination factor antitermination pQ binds at qut & enables RNAP to pQ qut read through terminator (from PR’ ) into late genes late So, transcription of late genes is induced by a delayed early regulatory proteins by λ LYSOGENY: AUTOGENOUS CIRCUIT LYSOGENY: PL & PR control gene expression through the entire early period with antitermination enabling transcription of delayed early genes early operators associated operators with both promoters repressed when λ repressor bound - RNAP transcription blocked & lytic cycle inhibited lytic cI mutants cannot mutants establish lysogeny (constitutive lytic) (constitutive λ “CLEAR” MUTANT GENES: cI, cII & cIII CLEAR” cI cII cIII • Mutants in cI & either of its cII /cIII positive regulators form clear plaques, not wildtype cloudy plaques - all mutants cannot establish lysogeny • wild-type phage prod...
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This note was uploaded on 03/26/2014 for the course MBB 321 taught by Professor Davidson during the Spring '11 term at Simon Fraser.

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