SARS-CoV Nucleocapsid Protein Binds To HUbc9, A Ubiquitin Conjugating Enzyme Of The Sumoylation System

SARS-CoV is a newly identified coronavirus (CoV) that causes severe acute respiratory syndrome (SARS). It is a single-stranded, positive-sense RNA virus, and belongs to the coronaviridae family only sharing 40%-60% homology with other members of the coronavirus family.Understanding the genome and exploring the function of the essential proteins of the SARS-CoV may aid us in elucidating the pathogenesis of the virus, and are the premise to search for the effective drugs and completely conquer the disease.The N protein of many RNA viruses is a multifunctional protein with important roles in the life cycles of the viruses. The SARS-CoV nucleocapsid (N) protein is an important structural and functional protein. sharing 20%-30% homology with the N protein of other members of the coronavirus family.It is a basic protein and the pI is 10.11, the theoretic molecular mass is 46kDa, 33 potential phosphorylation sites were identified in the N protein.A lysine-rich region in the C-terminal domain was predicted as the nuclear localization signal (NLS), and an SR-rich region was identified in the middle domain, which may be related to the RNA binding.To identify cellular proteins that interact with the SARS-CoV N protein in virus replication and assembly and to elucidate the possible involvement of N protein in SARS-CoV pathogenesis, a human lymphocyte cDNA library was screened using a yeast two-hybrid system assay. hUbc9, a ubiquitin conjugating enzyme of sumoylation system, was found to interact specifically with the N protein, implying the posttranslational sumoylation of the N protein. Mapping studies localized the critical N sequences for this interaction to amino acids 170-220, which includes the SR-rich motif. These results indicate that the interaction between SARS-CoV N protein and hUbc9 may regulate the replication of SARS-CoV or cell cycles, which might be involved in SARS pathogenesis. This is the first report to demonstrate the interaction of hUbc9 with a structural protein of plus-strand RNA viruses, indicating a new drug target for SARS-CoV.