RB1CC1 (RB1-inducible Coiled-Coil 1), a putative transcription factor implicated in the regulation of RB1 (retinoblastoma 1) expression, was recently identified in a screen for genes involved in multi-drug resistance to anticancer agents. Information about the RB1CC1 gene is limited, however, and its biological function is not determined. Here we report the isolation, characterization and mapping of the mouse RB1CC1 gene (Rb1cc1), together with further characterization of the human RB1CC1 gene. Mouse Rb1cc1 encodes 1588 amino acids, sharing 89% identity and key sequence motifs with its human counterpart. Rb1cc1 is expressed abundantly in heart and testis, with lower levels detected in lung and spleen. Immunohistochemical analysis revealed the Rb1cc1 and Rb1 proteins are co-localized in the cell nuclei of NIH3T3-3 cell and various mouse tissues. The human and mouse RB1CC1 genes, both of which contain 24 exons, span 74 kb on chromosome 8q11.2 and 57 kb on chromosome 1A2-4, respectively. Conserved sequence motifs and nuclear localization suggest that the RB1CC1 proteins function as transcription factors.