A novel centrosomal RING-finger protein, Dorfin, mediates ubiquitin ligaseactivity

We cloned a novel gene, Dorfin (double ring-finger protein), from human spi nal cord. The Dorfin mRNA transcript was 4.4 kb and expressed ubiquitously in many organs as well as in the central nervous system, including the spin al cord. Dorfin encoded 838 amino acid protein Dorfin, which contains two R ING-finger motifs and an IBR (in between RING-fingers) motif at its N-termi nus. Dorfin is a short-lived protein. Treatment with MG132, a potent protea some inhibitor, resulted in the accumulation of ubiquitinated Dorfin and Do rfin-associated cellular proteins in cultured cells. Dorfin bound specifica lly with human ubiquitin-conjugating enzymes UbcH7 and UbcH8 through the RI NG-finger/IBR domain. Partial deletion of the RING-finger/IBR domain elimin ated these interaction and ubiquitination activities. These results strongl y suggest that Dorfin is a new member of RING-finger type ubiquitin ligase. Dorfin is localized in the centrosome and probably functions in the microt ubule organizing centers. (C) 2001 Academic Press.