Cloning and Characterization ofZymomonas mobilisGenes Encoding Extracellular Levansucrase and Invertase

The genes encoding the extracellular levansucrase and invertase of Zymomonas mobilis have been cloned and sequenced. The levansucrase gene, sucZE2, spans 1269 bp and encodes an M(r) 46,790 polypeptide, and the invertase gene, sucZE3, is of 1239 bp and encodes an M(r) 46,110 polypeptide. The 5'-terminal sequences of both genes corresponded to the N-terminal amino acid sequences of the secreted levansucrase and invertase, implying that the secretion of both enzymes does not involve proteolytic processing of the N-terminals. Both enzyme molecules appear to carry no typical N-terminal secretion signal. Significant homology between sucZE2 and sucZE3 was observed, but both genes showed no homology to the gene encoding an intracellular invertase coexisting in Z. mobilis. Two genes, sucZE2 and sucZE3, are possibly placed in an operon because the expression of two genes were simultaneously controlled by the regulator gene zliE, previously identified.