15BIS101F2013MutatLect15

In these instances dna glycosylases are use to remove

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Unformatted text preview: Expression R.L. Rodriguez 41 Excision Repair of DNA Damage Repair of Pyrimidine Dimers BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 42 E. coli Excision Repair uvrA detects the distortion in the DNA and guides uvrB uvrB to the damaged site. to uvrA dissociates and uvrC uvrC binds uvrB at the damaged uvrB site. site. uvrB and uvrC makes cuts uvrC about 12 bases apart in the damaged DNA strand. damaged Helicase unwinds the 12mer from the helix. DNA polymerase I DNA synthesizes new DNA in the gap. gap. BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 43 Base Excision Repair of DNA Damage Base modifications are Base sometime too subtle to be recognized by the uvrA protein. In these instances, DNA glycosylases are use to remove damage bases. damage apurinic site (AP) BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 44 Deficiencies in DNA (excision) Repair Xeroderma pigmentosum is a rare heritable form of skin cancer in humans. Only about 1000 affected individuals world wide. Inheritance is autosomal recessive. recessive. The defect is in one of 8 The complementation groups (genes) involved in excision repair of UV induced DNA damage (XPA, XPB, XPC, XPD, damage XPA, XPE, XPF, XPG, and POLH) Complementation group XPC Complementation XPC is the most common and XPG is XPG associated with neurological disorders. disorders. BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 45 Molecular Mechanism of Mutation Mutation by “Slippage” Mutation “Slippage” in DNA Replication BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 46 Errors in DNA Replication: Slippage 13 b 13 b 12 b 15 b BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 47 Errors in DNA Replication: Strand Slippage During DNA replication, the nascent or template strand may During slip and add a base on one strand (nascent) or delete a base on the template strand. on BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 48 Fragile X Syndrome Fragile X (Xq27.3 ) is the most common inherited form of mental retardation, occurring in 1 of every 1200 males and 1 of every 2500 females. In 1991, the fragile X gene (FMR1) was characterized and found to contain a tandemly repeated trinucleotide sequence (CGG) near its 5' end. The mutation responsible for fragile X syndrome involves expansion of this repeat segment. The number of CGG repeats in the FMR1 genes of the general population v...
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