Excision repair in dna

Excision repair of DNA in humans and prokaryotes.

1. EXCISION REPAIR IN dna Presented by D.Irene 16PGZ001 M.Sc.Zoology ( spl in biotechnology) Lady Doak College, Madurai.

2. INTRODUCTION Cellular metabolism UV exposure Ionising radiation Chemical exposure Replication errors

3. Types of repair mechanisms

4. Dna excision repair By cut and patch mechanism Removes bulky lesions (pyrimidine dimers)

5. BASE EXCISION REPAIR IN Escherchia coli By DNA glycosylases . Recognition of the lesion in DNA Removes the base outside the helix and detaching it Creates AP site AP endonucleases produces single nucleotide gap Gap is filled by DNA polymerase I DNA ligase joints the backbone

6. http://gizmodo.com/dna-repair-earned-the-nobel-prize-in-chemistry-and-her-1735347676

7. BASE EXCISION REPAIR IN humans Recognition of the lesion in DNA the oxo G repair enzyme hOGG1 first binds non specifically to DNA the oxoG is extruded from the double helix into a “G specific pocket” the oxoG is inserted deeply into a lesion recognition pocket ( oxoGpocket ) on the enzyme.

8. Short patch repair -the enzymes involved - glycosylase-associated β- lyase (apurinic/apyrimidinic endonuclease) DNA polymerase β replaces the missing nucleotide, and the DNA ligase 3–XRCC1 complex seals the gaps in the sugar–phosphate backbone XRCC -“X-ray repair cross complementing rodent repair deficiency

9. Long patch repair APE1 makes an incision 5′ to the abasic site 2–10 nt are excised by FEN-1. DNA polymerase δ or ε for long patch repairs DNA ligase 1 for long patch repairs. FEN1 flap endonuclease 1

10. Nucleotide excision repair in Escherchia coli By multienzyme complex – ABC exinuclease Uvr A Uvr B Uvr C 3 subunits

11. 2 Uvr A and Uvr B attaches to the damaged site Uvr A leaves DNA & allows Uvr C ( Uvr BC complex) Uvr BC cuts the polynucleotide results in 12 nucleotide excision excised DNA is removed & Uvr C leaves Uvr B remains and prevents the pairing of single strand DNA gap is filled by polymerase I and backbone is joined by Ligase. Mechanism of Nucleotide excision repair

12. Nucleotide excision repair in HUMANS Removes bulges from thymine–thymine dimers induced by UV irradiation Six repair factors RPA XPA XPC TFIIH XPG XPF/ERCC1

13. MECHANISM DNA is recognised by RPA, XPA, XPC, and the TFIIH complex XPB and XPD unwinds the DNA double helix incision is made on the 3′ side of the damage, by an endonuclease (XPG) Another incision is made by a second endonuclease (XPF-ERCC1) on the 5′ side of the damage DNA polymerase ε or DNA polymerase δ, PCNA, RFC, and RPA for repair synthesis gap in the DNA backbone is closed by DNA ligase I. TFIIH-XPB &XPD RFC- Replication factor C Replication protein A PCNA- Proliferating cell nuclear antigen

14. Types of nucleotide repair Transcription coupled pathway Global genomic pathway

15. Xeroderma pigmentosum A child with xeroderma pigmentosum . Note the abnormal dark pigmentation in parts of the body exposed to sunlight

16. reference Ajoy paul .,Textbook of cellular and molecular biology., 4 th edition.,books and allied publishers.,2015.,pg 1077-1087. Lizabeth A. Allison., Fundamental Molecular Biology., blackwell publishing.,2007., Australia., pg 152-169.