The product of the retinoblastoma-related human gene Rb2/p130 is highly homologous with the product of the retinoblastoma tumor suppressor gene (pRb) and Rb-related p107. this homology is shared mainly in the pocket domain, a region that seems to play a key role in the functions of these proteins. Here we report the molecular cloning and initial characterization of the cDNA encoding the murine homologue of the human Rb2/p130 gene product. The 4.8-kb cDNA encodes a protein of 1125 amino acids that shows 90% indentity to that of the human protein. The Rb2/p130 mRNA is found to be expressed in all of the adult mouse tissues examined, with the highest level being detected in kidney and skeletal muscle. For the protein characterization, we used a polyclonal antibody raised against the COOH terminus of the human Rb2/p130 protein that also recognizes the mouse protein. In developing mouse embryos, the Rb2/p130 protein is expressed as early as day 10 of gestation and reached a peak of expression around day 13 of gestation, implying a developmental regulation of the Rb2/p130 gene in murine ontogeny.