Heterotetramer of two type I and two type II keratins. In skin, only expressed in the suprabasal cells of tail scale epidermis. Suprabasally expressed in stratified squamous epithelia and also in the posterior unit of the complex filiform papillae of tongue. Expressed in rare anatomical sites in which an orthokeratinized stratum corneum would be too soft and a hard keratinized structure would be too rigid to meet the functional requirement of the respective epithelia. mRNA synthesis is suppressed during retinoic acid-mediated orthokeratotic conversion of tail scale epidermis. There are two types of hair/microfibrillar keratin, I (acidic) and II (neutral to basic). Belongs to the intermediate filament family.