A Leuconostoc mesenteroides NRRL B-512 F levansucrase gene, (levS), was isolated, sequenced and cloned in Escherichia coli. The recombinant enzyme was shown to be a fructosyltransferase producing a polymer identified by (13)C-NMR as levan. Based on sequence analysis, we found that this levansucrase is a mosaic protein, bearing structural features of glucosyltransferases in the amino and carboxy terminal regions similarly to inulosucrase from Leuconostoc citreum. The phylogenetic analysis of the C-terminal region domain of levansucrases from L. mesenteroides demonstrates that they group together into a novel putative sub-family of genes and evolved long before all other glucosyltransferases, while their catalytic domain structure is species related.