Nucleobindin (Nuc) was first identified as a secreted protein of 55 kD that promotes production of DNA-specific antibodies in lupus-prone mice with the lymphoproliferation (lpr) mutation (Kanai et al., 1993). These mice produce large amounts of antibody against both single-stranded and double-stranded DNA (Theofilopoulos and Dixon, 1985). The primary defect is a deficiency in expression of the Fas gene. Analysis of cDNA that encodes mouse Nuc demonstrated that the protein is composed of a signal peptide, a DNA-binding site, 2 calcium-binding motifs, and a leucine zipper (Miura et al., 1992).

Miura et al. (1996) cloned human NUC, which encodes a deduced 461-amino acid peptide. A 2.4-kb NUC transcript was expressed in all organs examined.