Molecular Analysis of the Capsule Gene Region of Group A Streptococcus: the hasAB Genes Are Sufficient for Capsule Expression

Enzymes directing the biosynthesis of the group A streptococcal hyaluronic acid capsule are encoded in the hasABC gene cluster. Inactivation of hasC, encoding UDP-glucose pyrophosphorylase in the heavily encapsulated group A streptococcal strain 87-282, had no effect on capsule production, indicating that hasC is not required for hyaluronic acid synthesis and that an alternative source of UDP-glucose is available for capsule production. Nucleotide sequence and deletion mutation analysis of the 5.5 kb of DNA upstream of hasA revealed that this region is not required for capsule expression. Many (10 of 23) group A streptococcal strains were found to contain insertion element IS1239′ approximately 50 nucleotides upstream of the −35 site of the hasA promoter. The presence of IS1239′ upstream of hasA did not prevent capsule expression. These results elucidate the molecular architecture of the group A streptococcal chromosomal region upstream of the has operon, indicate that hasABC are the sole components of the capsule gene cluster, and demonstrate that hasAB are sufficient to direct capsule synthesis in group A streptococci.

介导A群链球菌（group A streptococcal）透明质酸荚膜（hyaluronic acid capsule）生物合成的酶类由hasABC基因簇（hasABC gene cluster）编码。在高荚膜A群链球菌菌株87-282中，对编码UDP-葡萄糖焦磷酸化酶（UDP-glucose pyrophosphorylase）的hasC进行失活处理后，荚膜生成未受影响，这表明hasC并非透明质酸合成所必需，且存在可替代的UDP-葡萄糖来源用于荚膜合成。对hasA上游5.5 kb DNA区域开展核苷酸序列分析与缺失突变实验后发现，该区域并非荚膜表达所必需。研究发现，23株A群链球菌菌株中有10株在hasA启动子（hasA promoter）的-35位点上游约50个核苷酸处携带插入元件IS1239′（insertion element IS1239′）。hasA上游存在IS1239′并不会阻碍荚膜表达。上述结果阐明了has操纵子（has operon）上游A群链球菌染色体区域的分子结构，证实hasABC是荚膜基因簇的唯一组成部分，并证明hasAB足以介导A群链球菌的荚膜合成。