The p95 gene (identical to NBS1 and nibrin) is a member of the hMre11/hRad50 double-strand break complex (MRN complex). This protein complex has been implicated in Nijmegen breakage syndrome, an autosomal recessive disorder marked by increased cancer incidence, cell cycle checkpoint deficits, and ionizing radiation sensitivity, thus revealing a direct molecular link between double-strand break repair and cell cycle checkpoint functions. In case of infection by adenovirus E4, the MRN complex is inactivated and degraded by viral oncoproteins, thereby preventing concatenation of viral genomes in infected cells. NBS1 is expressed ubiquitously and presents high levels in testis.