Natural Occurrence of Nuc in the Sera of Autoimmune-Prone MRL/lpr Mice

We previously established a clone of cells termed KML₁-7 which produces a soluble factor that boosts anti-DNA antibody production both in vitro and in vivo across the H-2 barrier. By using the purified protein, termed nucleobindin (Nuc), we cloned cDNA and produced recombinant (r) Nuc in E.coli. Although the purified rNuc showed biological activities such as anti-DNA antibody boosting and DNA binding, there was no evidence that Nuc is really associated with autoimmune status in lupus-prone MRL/lpr mice. Here we report that identification of Nuc was successful from the sera of MRL/lpr mice, but not from those of the substrain MRL/n mice, which show no apparent autoimmune syndrome at the same age of MRL/lpr mice, by means of immunochemical as well as N-terminal amino-acid sequencing methods.