Keratin 13 is a protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 that in humans is encoded by the KRT13 gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

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Keratin 13 is a type I cytokeratin

Type I cytokeratin

Type I keratins constitutes the Type I intermediate filaments of the intracytoplasmatic cytoskeleton, which is present in all mammalian epithelial cells...

, it is paired with keratin 4

Keratin 4

Keratin, type I cytoskeletal 4 also known as cytokeratin-4 or keratin-4 is a protein that in humans is encoded by the KRT4 gene....

 and found in the suprabasal layers of non-cornified stratified epithelia. Mutations in the gene encoding this protein and keratin 4 have been associated with the autosomal dominant disorder White Sponge Nevus

White sponge nevus

White sponge nevus , also known as Cannon's disease, Hereditary leukokeratosis of mucosa and White sponge nevus of Cannon, is an autosomal dominant skin condition...

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K13 is negative in buccal epithelium.