The function of HAS1 (hyaluronan synthase 1, Ensembl gene identifier ENSG00000105509) is as follows. Catalyzes the addition of GlcNAc or GlcUA monosaccharides to the nascent hyaluronan polymer. Therefore, it is essential for the synthesis of hyaluronan, a major component of most extracellular matrices that has a structural role in tissue architecture and regulates cell adhesion, migration and differentiation. This is one of the isozymes catalyzing that reaction. Also able to catalyze the synthesis of chito-oligosaccharide depending on the substrate (By similarity). .