Zinc finger protein 330
midbody
Molecular cloning of a zinc finger autoantigen transiently associated with interphase nucleolus and mitotic centromeres and midbodies. Orthologous proteins with nine CXXC motifs highly conserved from nematodes to humans.
We have cloned a novel human autoimmune antigen in a patient suffering from rheumatoid arthritis with high levels of antibodies to the nucleolus organizer regions. Initially the human autoimmune serum was used to select a cDNA of 317 amino acids from a hamster expression library. Using the hamster DNA as a probe, we isolated the human homologous cDNA of 320 amino acids. Human and hamster polypeptides share a 95% amino acid homology. The deduced 36-kDa protein contains a putative amino-terminal NLS signal, nine cysteine-X-X-cysteine motifs highly conserved, and a carboxyl-terminal poly acidic region. Several homologous expressed sequence tags have been identified in data bases suggesting that orthologous proteins are present throughout evolution from worms to humans. A Drosophila expressed sequence tag was further completely sequenced for a full-length protein with 60% amino acid identity to the human homologue. Northern blot analysis revealed that this novel protein is widely distributed in human tissues with significantly higher expression levels in heart and skeletal muscle. Specific antibodies to the recombinant protein and transfection experiments demonstrated by immunofluorescence the localization of the protein predominantly but not exclusively to the nucleolus of interphase mammalian cells. In actinomycin D-treated cells the protein remains associated with the nucleolus but is not segregated, like other ribosomal factors such as upstream binding factor. In mitosis the protein was found to be associated with centromeres and concentrated at the midbody in cytokinesis. Transient distribution of this evolutionarily conserved zinc finger nucleolar autoantigen to the mitotic centromeres may provide the means for several aspects of cell cycle control and transcriptional regulation.