Positional cloning of the gene for Nijmegen breakage syndrome

Abstract

Nijmegen breakage syndrome (NBS), also known as ataxia-telangiectasia (AT) variant, is an autosomal recessive disorder characterized by microcephaly, growth retardation, severe combined immunodeficiency and a high incidence of lymphoid cancers. Cells from NBS patients display chromosome instability, hypersensitivity to ionizing radiation and abnormal cell-cycle regulation after irradiation, all of which are characteristics shared with AT. Recently, the NBS locus was mapped at 8q21 by two independent approaches, complementation studies and linkage analysis. Here, we report the positional cloning of the NBS gene, NBS1, from an 800-kb candidate region. The gene comprises 50 kb and encodes a protein of 754 amino acids. The amino-terminal region of the protein shows weak homology to the yeast XRS2, MEK1, CDS1 and SPK1 proteins. The gene is expressed at high levels in the testes, suggesting that it might be involved in meiotic recombination. We detected the same 5-bp deletion in 13 individuals, and conclude that it is likely to be a founder mutation.

Structure of a Second BRCT Domain Identified in the Nijmegen Breakage Syndrome Protein Nbs1 and its Function in an MDC1-Dependent Localization of Nbs1 to DNA Damage Sites

“…Noticeably, the majority of patients with NBS have a deletion mutation of NBS1, which splits the Nbs1 protein at the beginning of BRCT2, giving rise to the p26 (1-218 aa) and p70 (221-754 aa) proteins. 8,9,22 While the secondary-structure elements of XNbs1 are similar to other known BRCT domains, we also notice a significant difference. Unlike the typical BRCT motif, there is a long insertion in XNbs1.…”

Nucleoside analogs: molecular mechanisms signaling cell death

“…ATM and the Mre11-Rad50-Nbs1 (MRN) complex are DNA damage response molecules closely associated with the repair of double-strand breaks (D'Amours and Jackson, 2002;Stracker et al, 2004), although several lines of evidence suggest that these molecules may also be involved in the response to stalled replication forks. Dysfunction of ATM or the MRN complex subunits results in embryonic lethality in eukaryotes (Xiao and Weaver, 1997;Luo et al, 1999;Zhu et al, 2001a) and hypomorphic mutations are associated with a variety of human disorders, including ataxia-telangiectasia (AT), ataxia-telangiectasia-like disorder (ATLD) and Nijmegen breakage syndrome (NBS, Carney et al, 1998;Matsuura et al, 1998;Varon et al, 1998;Stewart et al, 1999;Shiloh, 2006), suggesting their involvement during normal DNA replication. At the molecular level, the MRN complex associates with chromatin in an S phasespecific manner (Mirzoeva and Petrini, 2001) and binds with RPA (Robison et al, 2004;Olson et al, 2007).…”

Mutations of a novel human RAD54 homologue, RAD54B, in primary cancer

“…The ®rst hint that defects in recombinational repair contribute to tumor development came from the association of breast tumor susceptibility gene products BRCA1 and BRCA2 with hRAD51 (Scully et al, 1997;Sharan et al, 1997). Subsequently, NBS1, a member of the hMRE11/ hRAD50 recombination protein complex, was shown to be mutated in Nijmegen breakage syndrome, characterized by increased cancer incidence and ionizing radiation sensitivity (Varon et al, 1998;Carney et al, 1998;Matsuura et al, 1998). However, there is no direct evidence that cancer occurs through defects in repair processes involving homologous recombination.…”