The serotype a-specific polysaccharide antigen ofActinoba-cillus actinomycetemcomitansis an unusual sugar, (GDP)-6-deoxy-D-talose is the activated sugar nucleotide form of 6-deoxy-D-talose, which has been identified as a constituent of only a few microbial polysaccharides. In this paper, we identify two genes encoding GDP-6-deoxy-D-talose synthetic enzymes, GDP-a-D-mannose 4,6-dehydratase and GDP-4-keto-6-deoxy-D-mannose reductase, in the gene cluster required for the biosynthesis of serotype a-specific polysaccharide anti-gen from A. actinomycetemcomitansSUNYaB 75
