**1. Introduction**

124 DNA Repair

Petalcorin MI, Galkin VE, Yu X, Egelman EH, Boulton SJ. 2007 Stabilization of RAD-51-DNA

Qiao GB, Wu YL, Yang XN, Zhong WZ, Xie D, Guan XY, Fischer D, Kolberg HC, Kruger S,

Rahan R et al., Links between DNA double strand break repair and breast cancer: accumulating evidence from both familiar and nonfamilial cases. *Cancer Lett.* 2007 248: 1-17 Rajendra E. and Venkitaraman A. R. Two modules in the BRC repeats of BRCA2 mediate

Rogakou E. Megabase chromatin domains involved in DNA double strand breaks *in vivo*. J.

Rowling PJ, Cook R, Itzhaki LS. 2010 Toward classification of BRCA1 missense variants using a biophysical approach. *J Biol Chem.* JBC 285(26): 20080–20087 San Filippo J, Sung P, Klein H. Mechanism of eukaryotic homologous recombination. *Annu* 

Schild D, Wiese C. Overexpression of RAD51 suppresses recombination defects: a possible mechanism to reverse genomic instability. *Nucleic Acids Res.* 2010 38 1061-70 Seviour E & Lin S-Y 2010 Aging 2 900-907 The DNA damage response: Balancing the scale

Shivji MK, Mukund SR, Rajendra E, Chen S, Short JM, Savill J, Klenerman D, Venkitaraman

Slupianek A. Schmutte C., Tombline G., Nieborowska-Skorska M., Hoser G., Nowicki M.O.

Sonoda E, Sasaki MS, Buerstedde JM, Bezzubova O, Shinohara A, Ogawa H, Takata M,

Starita LM, Parvin JD. The multiple nuclear functions of BRCA1: transcription,

Tsuzuki T, Fujii Y, Sakumi K, Tominaga Y, Nakao K, Sekiguchi M, Matsushiro A,

Venkitaraman A.R. Linking the cellular functions of BRCA genes to cancer pathogenesis and

Vigneron A, Vousden KH. p53, ROS and senescence in the control of aging. *Aging (Albany* 

West SC. Molecular views of recombination proteins and their control. *Nat Rev Mol Cell Biol.*

Williams RS, Chasman DI, Hau DD, Hui B, Lau AY, Glover JN. Detection of protein folding

defects caused by BRCA1-BRCT truncation and missense mutations. *J. Biol. Chem.*

homologs, resulting in drug resistance. *Mol. Cell* 2001 8: 795-806.

chromosomal breaks prior to cell death. 1998 EMBO J 17 598-608

embryonic mice. *Proc Natl Acad Sci U S A*. 1996 93: 6236-6240

ubiquitination and DNA repair. *Curr Opin Cell Biol* 2003, 15: 345-50 Stürzbecher HW, Donzelmann B, Henning W, Knippschild U, Buchhop S. p53 is linked

AR. The BRC repeats of human BRCA2 differentially regulate RAD51 binding on single- versus double-stranded DNA to stimulate strand exchange. *Proc Natl Acad* 

Pierce A.J. Fishel R. and Skorski T. BCR/ABL regulates mammalian RecA

Yamaguchi-Iwai Y, Takeda S. Rad51-deficient vertebrate cells accumulate

directly to homologous recombination processes via RAD51/RecA protein

Yoshimura Y, MoritaT. Targeted disruption of the Rad51 gene leads to lethality in

*Acad Sci U S A*. 104: 8299–8304

*Res.* 2010, 38: 82–96

Cell Biol. 1999, 146 905-916

*Rev Biochem*. 2008 77 229

between cancer and ageing;

*Sci U S A.* 2009 106 13254–13259

interaction. *EMBO J.* 1996 **15:**1992-2002.

treatment. *Ann.Rev. Pathol.* 2009 4: 461-487

*NY)*, 2010 2:471-4.

2003, 278: 53007-16

2003 4:435-45.

filaments via an interaction domain in Caenorhabditis elegans BRCA2. *Proc Natl* 

Stuerzbecher HW. High-level expression of Rad51 is an independent prognostic marker of survival in non-small-cell lung cancer patients. *Br J Cancer.* 2005, 93:137-43.

structural and functional interactions with the RAD51 recombinase. *Nucleic Acids* 

Reactive oxygen species, ionizing radiation and alkylating agents can attack on DNA resulting in single or double strand breaks, generation of abasic sites, base and sugar lesions [1]. Double-strand breaks (ds breaks) are repaired by two different types of mechanism. One type takes advantage of proteins that promote homologous recombination (HR) to obtain instructions from the sister or homologous chromosome for proper repair of breaks. The other type permits joining of ends even if there is no sequence similarity between them. The latter process is called non-homologous end joining (NHEJ).The process by which complex single-strand breaks (those that cannot be directly religated) are repaired (SSBR) in some ways resembles NHEJ. Here we shall mainly discuss the mechanism of base excision repair (BER) of SSBR.
