An isolated and purified human nucleoprotein containing the amino acid sequence of SEQ ID NO:1; a polynucleotide encoding this protein; and an antibody against this protein. The above protein and antibody are useful in diagnosing and treating the pathogenic conditions of cancer, etc. The above polynucleotide is usable in acquiring the protein in a large amount. By screening a low-molecular weight compound binding to this protein, drugs of a novel type (antitumor agents, etc.) can be searched for.