Characterization of the fructosyltransferase gene of Actinomyces naeslundii WVU45

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.