Oral actinomycetes produce fructosyltransferase (FTF) enzymes which convert
sucrose into polymers of D-fructose, known as levans, and these polymers a
re thought to contribute to the persistence and virulence of the organisms.
A gene encoding FTF was isolated from Actinomyces naeslundii WVU45; the de
duced amino acid sequence showed significant similarity to known levansucra
ses of gram-negative environmental isolates but was less similar to FTFs fr
om gram-positive bacteria. A transcriptional start site was mapped by prime
r extension 70 bp 5' from the putative start codon, Promoter fusions to a c
hloramphenicol acetyltransferase gene were used to confirm that there was a
functional promoter driving ftf expression and to show that sequences loca
ted 86 to 218 bp upstream of the transcription initiation site were require
d for optimal ftf expression. Quantitative slot blot analysis against total
RNA from cells grown on different sugars or from different growth phases r
evealed that ftf was constitutively transcribed. Thus, the A. naeslundii FT
F is more similar in primary sequence and the regulation of expression to l
evansucrases of gram-negative bacteria than gram-positive bacteria.