| Modification Notes |
TOPORS (topoisomerase I binding, arginine/serine-rich), also known as LUN, RP31, P53BP3 or TP53BPL, is a 1,045 amino acid protein that contains one RING-type zinc finger and localizes to discrete nuclear foci. Expressed in a variety of tissues with highest expression in testis, TOPORS functions as a ubiquitin E3 ligase that, via its RING domain, can ubiquitinate proteins such as p53, thereby targeting them for proteasomal degradation. TOPORS expression can be induced by genotoxic agents (compounds that damage DNA), such as camptothecin and cisplatin, suggesting an important role for TOPORS in DNA damage repair pathways. In addition, TOPORS levels are decreased in lung and colon cancers, implicating TOPORS as a possible tumor suppressor. Defects in the gene encoding TOPORS are the cause of retinitis pigmentosa type 31 (RP31), a degenerative disease characterized by a loss of peripheral and, eventually, central vision. |