Y. Tsukioka et al., IDENTIFICATION OF A 4TH GENE INVOLVED IN DTDP-RHAMNOSE SYNTHESIS IN STREPTOCOCCUS-MUTANS, Journal of bacteriology, 179(13), 1997, pp. 4411-4414
had isolated three genes (rmlA, rmlB, and rmlC) involved in dTDP-rhamn
ose synthesis in Streptococcus mutans and found that three genes were
insufficient for dTDP-rhamnose synthesis (Y.Tsukioka, Y. Yamashita, T.
Oho, Y. Nakano, and T. Koga, J. Bacteriol. 179:1126-1134, 1997). The
rmlD gene of S. mutans, encoding the enzyme which catalyzes the last s
tep of dTDP-rhamnose synthesis, has been cloned and sequenced. The cel
l extract of Escherichia coli expressing the rmlD gene of S. mutans ex
hibited enzymatic activity corresponding to its counterpart in Shigell
a flexneri, a gram-negative bacterium. Rhamnose aas not detected in th
e cell wall preparation purified from the mutant in which the cloned g
ene was insertionally inactivated. Rabbit antiserum against S. mutans
serotype c-specific antigen did not react with autoclaved extracts fro
m the mutant. The rmlD gene product of S. mutans compensated for the i
ncompleteness of dTDP-rhamnose synthesis by the three previously isola
ted genes. These results indicate that the rmlD gene product is indisp
ensable for the dTDP-rhamnose pathway and subsequently for the synthes
is of serotype-specific antigen in S. mutans. Furthermore, conservatio
n of the rmlD gene in Streptococcus species was demonstrated by Southe
rn blot analysis.