MOLECULAR-CLONING OF NUCLEOBINDIN, A NOVEL DNA-BINDING PROTEIN THAT CONTAINS BOTH A SIGNAL PEPTIDE AND A LEUCINE ZIPPER STRUCTURE

We have previously reported that KML1-7 cells cloned from a lupus-prone MRL/1 mouse produced a soluble factor that preferentially expanded anti-DNA antibody production across the H-2 barrier. We purified this factor, a 55 kD protein that we termed nucleobindin (Nuc), and obtained its cDNA clone. Although the gene for Nuc encodes a signal peptide and, in fact, Nuc was identified as a secreted protein, Nuc had a DNA binding property. The putative polypeptide predicted from the cDNA sequence featured a signal peptide, a leucine zipper structure and a basic amino acid-rich region. The DNA-binding property of Nuc was destroyed by deletion of either the leucine zipper structure or the basic amino acid-rich region. The amino acid sequences of Nuc are highly conserved between mouse and human. We discuss the possible role of Nuc in autoimmunity. © 1992 Academic Press, Inc.