Hrap12, a human ubiquitin-like nuclear protein that associates with human rad51/rad52 proteins

The RAD51/RAD52-dependent DNA repair pathway is involved in DNA recombination and DNA double strand break repair in yeast. Although many proteins in the RAD51/RAD52-dependent DNA repair pathway have been identified in yeast, novel protein(s) that function with RAD51/RAD52 may also exist in humans. Using a yeast two-hybrid system, we have identified a 12 kDa protein which associates with human RAD51 and RAD52 proteins. This protein is tentatively designated hRAP12 for human RAD51/RAD52-Associated Protein. hRAP12 shares significant amino acid homology with the yeast protein SMT3, which functionally associates with the yeast mitosis fidelity protein MIF2. MIF2, a homolog of mammalian centromere protein CENP-C, functions in mitotic spindle formation and chromosome segregation. hRAP12 also shares moderate homology with ubiquitin and several ubiquitin-like proteins, including the N-terminus of RAD23 protein, and an Ubiquitin Cross Reacting Protein (UCRP). Immunofluorescent analysis using antibodies generated from (His)₆-tagged hRAP12 proteins show that hRAP12 is mainly located in the nucleus. The hRAP12 mRNA is expressed in many human tissues, most highly in testis. hRAP12 gene is mapped on chromosome 2q32.2-33, and a related sequence may be located on chromosome 1q23-25.