Recognizes a 33kDa glycoprotein, identified as nucleophosmin (NPM). It is predominantly localized in the nucleus of cells in most tissues. NPM is involved in ribosomal assembly and rRNA transport. It is an abundant protein that is highly phosphorylated by Cdc2 kinase during mitosis. This phosphoprotein moves between the nucleus and the cytoplasm. It is thought to be involved in several processes including regulation of the ARF/p53 pathway. A number of genes are fusion partners, in particular the anaplastic lymphoma kinase gene on chromosome 2. Mutations in exon 12 affecting the C-terminus of the protein are associated with an aberrant cytoplasmic location. Mutations in this gene are associated with acute myeloid leukemia. The antibody is a useful aid for classification of acute myeloid leukemia.