HYALURONIC-ACID SYNTHESIS OPERON (HAS) EXPRESSION IN GROUP-A STREPTOCOCCI

The has operon is composed of three genes, hasA, hasB, and hasC that e ncode hyaluronate synthase. UDP-glucose dehydrogenase, and presumptive ly UDP-glucose pyrophosphorylase, respectively. Expression of the has operon was shown to be required for the synthesis of the hyaluronic ac id capsule in group A streptococci. Previous studies indicated that so me group A and group C streptococcal strains produce the hyaluronic ac id capsule, while others do not. In addition, it was observed that enc apsulated strains cultured in stationary phase of growth lose the hyal uronic acid capsule. Therefore, the molecular mechanisms controlling t he expression of the hyaluronic acid capsule in group A streptococci w as investigated. In this study, it was determined that all encapsulate d and unencapsulated strains of group A streptococci as well as encaps ulated group C streptococci analyzed possess the has operon locus. The acapsular phenotype was accounted for by the absence of hyaluronate s ynthase activity in the membrane and not the production of extracellul ar hyaluronidase. A has operon mRNA transcript was not expressed by un encap sulated strains of group A streptococci, whereas encapsulated st rains of group A streptococci grown to mid to late exponential phase p roduced the hyaluronate capsule, as well as has operon mRNA. However, as the streptococci entered the stationary phase of growth, they becam e acapsular and this was concomitant with the loss of has operon mRNA transcript. These results were confirmed by primer extension analyses of RNA isolated from encapsulated and unencapsulated strains of group A streptococci as well as RNA prepared from encapsulated strains cultu red in exponential and stationary phases of growth. Thus, the loss of has operon mRNA in unencapsulated group A streptococci, as well as gro wth phase regulation occurs at the previously mapped has operon promot er. These data suggested that the synthesis of the hyaluronic acid cap sule for group A streptococci may be controlled by transcriptional mec hanisms.