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Chi sequence

molecular biology

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Chi sequence

  1. 1. MOLECULAR BIOLOGY
  2. 2. INTRODUCTION  Crossover hotspot instigator(CHI).  Chi sites are referred to as "recombination hot spots“.  Chi sites was originally discovered in bacteriophage lambda, a virus that infects E. coli, but is now known to occur about 1000 times in the E. coli genome.
  3. 3.  A Chi site or Chi sequence is a short stretch of DNA in the genome of a bacterium near which homologous recombination occur.  Homologous recombination occurs between sequences that are nearly identical.
  4. 4.  The Chi site is unique to each group of closely related organisms.  Eg: 5'-GCTGGTGG-3‘(in salmonella).  The Chi sequence serves as a signal to the RecBCD helicase-exonuclease that triggers a major change in the activities of this enzyme.
  5. 5. CHI SITE MEDIATED HOMOLOGOUS RECOMBINATION BY RecBCD PATHWAYA STEP 1:
  6. 6.  STEP 2:
  7. 7. RecBCD : A COMPLEX ENZYME  It has endonuclease subunit(RecBCD) which cuts one DNA strand close to Chi sequence.  And DNA helicase activity (recD subunit). RecA:  Catalyzes strand exchange.
  8. 8. ROLE OF CHI SITE  Generating new gene/allelli. E.g: immunoglobulin rearrangement.  Intigration of a specific DNA element.  DNA repair.
  9. 9. Thank you

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