CK-39, or Keratin 39, type I, is a human gene encoded by KRT39. It may also be known as: Keratin, type I cytoskeletal 39; Cytokeratin-39; Keratin-39; K39; Type I hair keratin Ka35; KA35. The encoded protein has an amino acid length of 491 and a mass of 55.7 kDa. CK-39 is a member of the Intermediate filament family. Homologs of this gene exist in other organisms, including: Mouse, Rat.