week_8_lecture_2

2 on the sos response and on reca on like its action

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Unformatted text preview: ytic cycle likely when cells CII grown in rich medium grown • CII more stable & lysogeny likely when cells CII under starvation conditions - allows phage to wait until effective resources available for replication & packaging replication λ LYTIC CASCADE: SUMMARY SUMMARY -Cro binds OL and OR Cro and inhibits cI, cII, & cI cII cIII expression, and cIII turns-off early genes not needed for lysis not - pQ permits RNAP transcription of late genes that begin the lytic cascade lytic INDUCING λ PROPHAGE • λ induction dependent Weaver 2002 Molecular Biology Ed. 2 on the SOS response and on RecA on • Like its action on LexA, Like RecA also co-protease for λ repressor • RecA promotes λ RecA repressor self-cleavage releasing repressor from PL & PR and cro cro expressed expressed • Thus, DNA damage & cell Thus, stress “tell” λ to leave host cell before host cell dies dies RECALL THE SOS RESPONSE RESPONSE (error-prone bypass repair) • RecA also RecA involved in SOS involved response response • metabolic alarm metabolic system activated in response to DNA damage (UV, alkylating agents) or inhibition of replication (eg. mutations in dna dna genes) genes) • response response manifested as increased capacity to deal with damaged DNA Weaver 2002 Molecular Biology Ed. 2 Summary 1 • The immediate early/delayed early/late transcriptional switching in the lytic cycle of phage λ is controlled by antiterminators. • One of the two immediate early genes is cro, which codes for a repressor of the cI gene that allows the lytic cycle to continue • The other, N, codes for an antiterminator, that overrides the terminators after the N and cro genes. Transcription then continues into the delayed early genes. • One of the delayed early genes, Q, codes for another terminator (Q) that permits transcription of the late genes from the late promoter, PR’, to continue without premature termination Summary 2 • Phage λ establishes lysogeny by causing production of...
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