In the absence of KRT14, makes a bona fide, but ultrastructurally distinct keratin filament network with KRT5. Heterotetramer of two type I and two type II keratins (Probable). Forms a heterodimer with KRT14 (PubMed:24940650). Interacts with PLEC isoform 1C, when in a heterodimer with KRT14 (PubMed:24940650). Interacts with NOD2 (By similarity). Expressed strongly in the basal cell layer at the tips of rete-like prominences (RLPs) of adult dorsal tongue, outer root sheath (ORS) of hair follicle and skin epidermis (at protein level). Expressed in the skin at birth (at protein level) (PubMed:11408584). In neonatal mice, additional expression seen in the basal layer of the cornea, forestomach and esophagus (at protein level). During wound healing expression is suppressed by TGF-beta, TNF-alpha and to a lesser extent by epidermal and keratinocyte growth factors (EGF and KGF respectively). 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.