BCCIP (or TOK1) is isolated as a BRCA2- and CDKN1A (p21)-interacting protein and is implicated in homologous recombination (HR) pathway and inhibition of DNA replication stress. BCCIP is an evolutionarily conserved nuclear protein with multiple interacting domains. BCCIP deficiency in mice impaired embryonic and postnatal neural development, causing severe ataxia, cerebral and cerebellar defects, and microcephaly, which are associated with spontaneous DNA damage and subsequent cell death in the proliferative cell populations of the neural system during embryogenesis. BCCIP is essential for maintaining the transactivation activity of wild type p53 suggesting a potential role of BCCIP in cancer etiology.