Haspins is a protein family containing a distinctive C-terminal kinase domain and a divergent N-terminus. Haspin homologues occur within a diverse group of eukaryotes, including animals, plants and fungi, which suggests an early evolutionary origin. Haspin, a nuclear protein strongly expressed in male germ cells, is responsible for the phosphorylation of histone H3 at Thr-3. Depletion of Haspin RNA prevents normal alignment of chromosomes at metaphase, suggesting a crucial role for haspin during chromosome segregation. Expression of haspin also occurs in adult thymus and bone marrow, with weaker expression in adult prostate, intestine, lung, spleen, and lymph node. The gene encoding human haspin maps to chromosome 17p13.