Cross-linked envelope protein of keratinocytes. It is a keratinocyte protein that first appears in the cell cytosol, but ultimately becomes cross-linked to membrane proteins by transglutaminase. All that results in the formation of an insoluble envelope beneath the plasma membrane (By similarity). Expressed weakly in uterus. During early pregnancy, low expression detected in uterus at 1 dpc. Belongs to the cornifin (SPRR) family.