Glycosaminoglycan synthesis. The hyaluronic acid capsule is involved in the pathogenicity of group A Streptococci; it may be the major virulence determinant (By similarity). [hyaluronan](n) + UDP-N-acetyl-alpha-D-glucosamine = H(+) + N-acetyl-beta-D-glucosaminyl-(1->4)-[hyaluronan](n) + UDP N-acetyl-beta-D-glucosaminyl-(1->4)-[hyaluronan](n) + UDP-alpha-D-glucuronate = [hyaluronan](n+1) + H(+) + UDP Glycan biosynthesis; hyaluronan biosynthesis. Belongs to the NodC/HAS family. It is uncertain whether Met-1 or Met-25 is the initiator.