Molecular characterization of hasA from an operon required for hyaluronic acid synthesis in group A streptococci

The mechanism by which group A streptococci produce the antiphagocytic hyaluronate (hyaluronic acid) capsule is incompletely understood. Enzymes known to be essential for synthesis of this polysaccharide include the membrane-associated hyaluronate synthase as well as those required for production of the substrate sugars UDP-N-acetylglucosamine and UDP-glucuronic acid. In this study, a Tn916 insertion that inactivates hyaluronate synthetic activity was localized to a gene designated hasA in the hyaluronic acid synthesis operon. This gene has recently been preliminarily identified as the group A streptococcal hyaluronate synthase. The DNA sequence and transcription start site of hasA were determined, and the predicted HasA protein was shown to have characteristics of a membrane protein. Amino acid sequence homology suggests that HasA is related to a family of proteins involved in polysaccharide production and cell differentiation. Finally, in addition to the loss of hyaluronate synthase activity, the hasA::Tn916 insertion was demonstrated to correlate with a loss of UDP-glucuronic acid dehydrogenase activity. These results suggest that the genes required for hyaluronate synthase activity and production of the UDP-glucuronic acid substrate are transcribed as a unit in group A streptococci.