Recombination

Recombination：RecBCD、DNA basis、RecA、Process.

Recombination

• RecBCD
  • RecB
    • helicase+endonuclease
  • RecC
    • chi recognization
  • RecD
    • helicase
• DNA basis
  • 3' strand chi sequence
• RecA
  • A DNA-dependent ATPase
    • Have site for ATP binding and ATPase
  • In SOS: RecA-ATP cleaves LexA repressor
  • In DNA repair:
    • -Binds to ssDNA and dsDNA
    • -RecA-ssDNA complex: searches for “homology” along dsDNA.
• Process
  • Generates RecA binded 3' overhanging(D-looping)
    • 1. Rec BCD binds to DNA end and scann and unwind it at same time cleaves exposed ssDNA
      • 3' strand cleaved more than 5' strand
    • 2. SSB binds to 2 exposed single strands
    • 3. Rec BCD scann to chi sequence, at same time 3' strand cleaved to chi
    • 4. Chi sequence in 3' end will recruits RecA to cover further exposed 3' ssDNA
    • 5. Rec A bindes 3'ssDNA is undegredable by Rec BCD
      • This makes 5' strand more digested
        • generates RecA bonded 3' overhanging
  • Rec A mediated strand exchange
    • 1. form holyday junction
      • 1. recA binded(some cases my conain few ssB) 3' overhanging invade anther neighboring dsDNA by hybridizing with on of its strand
    • 2.branch migration occur
      • DNApol III elongates D loop 3' end, and replaces the front 3' homologous strand
      • The homologous 3' strand is hybridized to the original exposed 5' single strand
    • 3. Resolusion occur
      • by resolvasion complex
        • -RuvA tetramer fits within the junction point
          • junction binding
        • -RuvB (hexamer) binds on each side of Holliday junction, encircling the dsDNAs
          • branch migration
        • -RuvC (Resolvase) resolves Holliday junction by cleaving the non-crossover strand
          • two possible outcomes
            • Patch
              • cleaves left&right
            • Splice
              • cleaves upp&down
          • Ligase seal the nicks