Heterodimer of a type I and a type II keratin. KRT6 isomers associate with KRT16 and/or KRT17. Expressed in adult epithelia including the tongue, esophagus/trachea, eye and skin. Localized preferentially to the suprabasal layers of thickened epidermis in injured and chemically treated skin. By injury, and treatment of the skin with the phorbol ester PMA. There are two types of cytoskeletal and microfibrillar keratin, I (acidic) and II (neutral to basic) (40-55 and 56-70 kDa, respectively). Belongs to the intermediate filament family.