Centromere protein F (CENPF), also named mitosin, is a large human protein of 3113 amino acid residues. Its expression and localization are cell cycle-dependent. The protein levels are low in G1 phase but elevated from S to early M phase. CENPF is a nuclear matrix protein in interphase but is relocated to the kinetochore, the major site of microtubule attachment on chromosome, in M phase (1).