HAS1, HAS2 and HAS3 are HA synthase proteins that synthesize HA (hyaluro nan or hyaluronic acid). The extracellular matrix in most vertebrates expres HA, which is a high molecular weight linear polysaccharide composed of alter nating glucuronic acid and N-acetylglucosamine residues linked by beta-1,3 andbeta-1,4 glycosidic bonds. The three HAS genes show distinct patterns of expres sion during development and their protein products play significantly different roles in the formation of the HA matrix. Both HAS1 and HAS2 synthesise high molecular-weight HA, whereas HAS3 produces lower molecular weight HA. The expression of the three HAS isoforms is more prominent in growing cells than in resting cells and is differentially regulated by various stimuli suggest ing distinct functional roles of the three proteins. HAS2 mRNA shows pre dominant expression in chondrocytes and cartilage. The human HAS2 gene maps to chromosome 8q24.13
