Abstract
Nijmegen breakage syndrome (NBS) is a rare autosomal recessive genetic disorder characterized by immunodeficiency and cancer predisposition. The NBS cellular phenotype includes chromosomal instability, hyper-sensitivity to radiation and abnormal S phase checkpoints which is similar to Ataxia-telangiectasia(AT). NBS1 protein, product of the NBS gene, forms a complex with MRE11 and RAD50, and the RAD50/MRE11/NBS1 (R/M/N) complex plays a crucial role in DNA double strands break (DSB) repair. The human NBS1 has three functional regions. N-tarminus includes a fork head associated (FHA) domain and a BRCA1 C-terminus (BRCT) domain. In the central region, there are two serine residues at 278 and 343 that are phosphorylated by the ATM or ATR kinases. The C-tarminus includes MRE11 binding domain. We have reported that the R/M/N complex with functional NBS1 is essential for homologous recombination (HR) repair pathway. This suggested that NBS1 regulates the function of the complex by regulating both their subnuclear localization and enzymatic activities. To analyze functional domains of NBS1 in HR repair pathway, an SCneo reporter was introduced into HeLa or NBS patient cells. Then, mutant NBS1 was expressed in these cells, and HR activity was analyzed by transient expression of I-SceI endonuclease. It was found that C-tarminus and FHA domain of NBS1 is essential for regulation of nomal HR function.
