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Holliday vs. Meselson-Radding Models
- Holliday model: SYMMETRIC formation of heteroduplex DNA on BOTH chromatids
- Meselson-Radding: ASSYMETRIC recombination >>> leads to Assymetric heteroduplex DNA
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Recombination steps
- 1. Synapsis of chromosomes
- 1. Double Strand BREAK Formation
- 2. 5’ resection
- 3. Unstable strand invasion
- 4. Repair synthesis and Holliday Jxn
- 5. Crossover/Noncrossover
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Role of spo11
- Transesterase protein involved in meiosis
- Aids in recombination through Double stranded breaks
- These breaks aid in FORMING crossovers
- *Mre11 ENDONUCLEASE involved in cleaving of DS DNA also
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Failure to form crossover consequences
- 1. No homologue pairs formed
- 2. No aligning at metaphase plate
- 3. No SEGREGATION during meiosis
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Double Stranded break
- 1. Spo11 attached on one end, with other end with a free 3’ tail
- 2. Spo11 is released, taking with it 2 oligonucleotides, called spolligos
- 3. Once Spo11 released, the other end has a free 3’end tail as well
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Role of Rad51
- Involved in homology search to IDENTIFY homologous chromosomes
- Also role in REPAIR of damaged DNA
- Assembles on other side of DSB as the Dmc1
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Role of Dmc1
- Initiates stable STRAND INVASION
- Assembles on 3’ tail of a ssDNA break
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Role of Mnd1-Hop2 in homologous recombination
- Stabilizes interactions between homologous chromosomes
- Localizes to chromosomes independent of Dmc1 and Rad51
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Synapsis Initiation complex (SIC)
- Mediates synapsis, pairing and recombination
- Found B/w homologous chromosomes during replication
- Contain Zip1-3, which promote polymerization
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