<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>A protein often found as a cell surface marker on tumor cells.</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition><n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>Cytokeratin 19 is an intermediate filament subunit. Keratins belong to two families: acidic (type I) and basic (type II). As a rule they are coordinately synthesized in pairs so that one member of each family is expressed in epithelial cells. The most striking exception to this rule is the acidic keratin, KRT19. Also, although its alpha-helical central domain conforms to the canonical keratin structure, KRT19 uniquely lacks a C-terminal non-helical extension. (from OMIM 148020 and NCI)</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>