Alpha-1,3-xylosyltransferase, which elongates the O-linked xylose-glucose disaccharide attached to EGF-like repeats in the extracellular domain of target proteins by catalyzing the addition of the second xylose (, ). Known targets include Notch proteins and coagulation factors, such as F9 (, ).
Subcellular locations: Endoplasmic reticulum membrane