Type 1 keratin (Probable). Maintains postnatal tongue mucosal cell homeostasis and tissue organization in response to mechanical stress, potentially via regulation of the G1/S phase cyclins CCNE1 and CCNE2 (By similarity). Heterotetramer of two type I and two type II keratins. O-glycosylated; glycans consist of single N-acetylglucosamine residues. There are two types of cytoskeletal and microfibrillar keratin: I (acidic; 40-55 kDa) and II (neutral to basic; 56-70 kDa). Belongs to the intermediate filament family.