lecture_20

lecture_20 - 5 Error-free repair Synthesis-dependent strand...

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1 Lecture 20 Outline of lecture 20 SOS response, trans-lesion DNA synthesis E. coli DNA polymerase V Repair of double-strand DNA breaks Error-prone nonhomologous end joining Error-free repair Homologous recombination Gene conversion and postmeiotic segregation
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2 Translesion DNA synthesis Error prone repair In E. coli : SOS system Replication is stalled due to DNA damage The fidelity of DNA replication is relaxed so that the replication fork can bypass the damaged site.
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3 DNA polymerase V It lacks the 3’ to 5’ exonuclease activity Low processivity: it polymerases only few nucleotides Pol V is constitutively present but cannot bind PCNA (eukaryotic β clamp) Pol V is activated by ubiquitinilation. Ubiquitinilated Pol V can bind the PCNA. This is an example of posttranslational modification of a protein
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4 Repair of double-stranded breaks in DNA Error prone Nonhomologous end joining (NHEJ) KU70 and KU80 heterodimer binds to the broken DNA ends. Exonucleases generate blunt end. XRCC4 gene product and ligase IV.
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Unformatted text preview: 5 Error-free repair Synthesis-dependent strand annealing 6 Single-strand invasion E. coli RecA = eukaryotic Rad51 Rad51 associates with single-strand binding proteins forming Rad51 filament Rad51 filament is invasive Invades the sister chromatid to form a D-loop 7 Homologous recombination Initiated by creation of double-strand DNA break by staggered cut by Spo11 Rad51 and Dmc1 bind to single stranded DNA forming a Rad51 filament The filament searches for homologous DNA molecule Dmc1 is meiosis specific 8 Two pathways of homologous recombination (1) Crossover pathway (2) Non-crossover pathway 9 Gene conversion in N. crassa Gene conversion is nonreciprocal recombination It originates by repair of mismatches created by synthesis-dependent strand annealing 10 Gene conversion 6 wild type:2 mutant 2 wild type: 6 mutant Postmeiotic segregation in N. crassa Results from failure to repair a mismatch. 5 wild type:3 mutant 3 wild type: 5 mutant...
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This note was uploaded on 12/13/2009 for the course BIS 101 taught by Professor Simonchan during the Fall '08 term at UC Davis.

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lecture_20 - 5 Error-free repair Synthesis-dependent strand...

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