Types of dna recombination
- 1. Various types Of DNA Recombination Presented to: Dr. Tanzeela Riaz Presented by: Aiman Nisar L1S16BSMR0013
- 2. Introduction • “the rearrangement of genetic material, especially by crossing over in chromosomes or by the artificial joining of segments of DNA from different organisms”. • Occurs in both prokaryotes and eukaryotes.
- 4. Types 1. General or homologous recombination 2. Site-specific recombination 3. Illegitimate or non-homologous 4. Replicative recombination 5. Mitotic recombination
- 5. 1. Homologous/General Recombination • Occurs between homologous chromosomes • Both in prokaryotic and eukaryotic cells • Explaining models: 1. Holiday Model 2. Double strand break model
- 6. Double strand break model
- 11. 1. Homologous Recombination (OVERVIEW) • RecBCD Complex: • Exonuclease function (One chromosome remains intact, other has a double stranded break). • Helicase activity (moves along chromosome and opens it up, reaches chi site) • 3’ overank formed • Rec A: • Completely covers one strand • Makes chiasma of other strand
- 12. 1. Homologous Recombination (OVERVIEW) • RuvAB complex helps in branch migration • RuvC cleave chiasma junction • DNA Ligase seals nick
- 13. 2. Site Specific Recombination • This is observed between particular, very short, sequences, usually containing similarities. • Occurs in bacteriophages, bacteria, unicellular eukaryotes • Involves one enzyme only: • Recombinase (either serine or tyrosine)
- 18. 2. Site specific DNA Recombination (OVERVIEW) • Recombinase: • binds at RRS(Recombinase Recoginition Sites) present on both chromosomes • has OH- at the end that acts as nucleophile and interacts with phosphodiester bond of DNA • forms nick by cleaving between TAGC • swaps the segments
- 19. 2. Site specific DNA Recombination (OVERVIEW) • Serine Recombinase makes double stranded breaks in both chromosomes • Tyrosine Recombinase makes double stranded breaks in each recombinant strands of both chromosomes
- 20. 3. Non-homologous/Illegitimate Recombination • This type occurs between DNA molecules that are not necessarily similar. • In bacteria and the yeast integration of such DNA into the genome requires substantial sequence similarity between incoming DNA and the recipient site. • However, cells of other fungi, higher plants, and animals are able to integrate foreign DNA into their chromosomes with little or no sequence similarity.
- 22. 3. Non-homologous/Illegitimate Recombination (OVERVIEW) • Ku70,80 protein complex • recognizes site of broken DNA • Forms “DNA binding component” of DNA Dependent Protein Kinase(DNA-PK) • Encircles DNA preventing it from binding with unbroken DNA • Polymerases synthesize new DNA • Nucleases cleave and clean ends • XRCC4 stabilize DNA Ligase4
- 23. 4. Replicative Recombination/Replicative Transposition • Generates a new copy of a segment of DNA. • Many transposable elements use a process of replicative recombination to generate a new copy of the transposable element at a new location. • Copy and paste method
- 25. 5. Mitotic Recombination • This doesn’t actually happen during mitosis, but during interphase • The process is similar to that in meiotic recombination, and has its possible advantages • But it’s usually harmful and can result in tumors. • This type of recombination is increased when cells are exposed to radiation.
- 27. Thank You For Your Attention