Heterotetramer of two type I and two type II keratins. Keratin-4 is generally associated with keratin-13. Detected in the suprabasal layer of the stratified epithelium of the esophagus, exocervix, vagina, mouth and lingual mucosa, and in cells and cell clusters in the mucosa and serous gland ducts of the esophageal submucosa. Expressed widely in the exocervix and esophageal epithelium, with lowest levels detected in the basal cell layer. Belongs to the intermediate filament family. Note: This description may include information from UniProtKB.