A novel cytosolic phosphoprotein, DP58 induced in bone marrow-derived dendritic progenitors was found in this study to be constitutively expressed at a very high level in neuronal nuclei. Amplified cDNA confirmed by sequencing to be DP58 was present only in brain tissue, and DP58-like protein was expressed in neurons as a 52 kDa nuclear protein, phosphorylated primarily at the serine residues. In contrast, its isoform in dendritic progenitors appeared as a 58 kDa inducible protein with phosphorylation at serine, threonine and tyrosine residues. Although protein markers common to brain and hematopoietic cells are known, no report was found on constitutive expression in neuronal nuclei of DP58, an inducible Pro-myloid marker. The sequence of DP58 reveals ankyrin repeats present in a wide spectrum of interacting proteins including NF-kappaB-binding BCL3, a predominantly nuclear protein of I-kappaB family. The contrasting phosphorylated forms of DP58 suggest a distinct physiological role in neuronal cells and early dendritic progenitors.