BIOLOGICAL FUNCTION OF THE DTDP-RHAMNOSE SYNTHESIS PATHWAY IN STREPTOCOCCUS-MUTANS

We have cloned a new gene locus that comprises three genes concerned w ith the biosynthesis of the serotype c-specific polysaccharide antigen in Streptococcus mutans. The genes encode proteins exhibiting signifi cant homolog to the rfbA, rfbB, and rfbD gene products that are involv ed in the anabolism of dTDP-L-rhamnose from D-glucose-1-phosphate. Thi s anabolism pathway pertains to biosynthesis of the O antigen of lipop oly-saccharide in gram-negative bacteria, The cell extract of Escheric hia coli expressing each of the cloned genes of S. mutans exhibited en zymatic activity corresponding to the homologous counterpart of the rf b gene products, Rhamnose was not detected in the cell wall preparatio n purified from the mutant in which each of the three cloned genes was insertionally inactivated, Rabbit antiserum against S. mutans serotyp e c-specific antigen did not react with the autoclaved extracts from t hese mutants, These results indicate that the gene products identified in the present study are involved in the dTDP-L-rhamnose synthesis pa thway and that the pathway relates to the biosynthesis of the serotype -specific polysaccharide antigen of S. mutans. Southern hybridization analysis revealed that genes homologous to the cloned genes involved i n the dTDP-L-rhamnose synthesis pathway were widely distributed in a v ariety of streptococci. This is the first report of the biological fun ction of the dTDP-rhamnose pathway in streptococci.