THE SACB AND SACC GENES ENCODING LEVANSUCRASE AND SUCRASE FORM A GENE-CLUSTER IN ZYMOMONAS-MOBILIS

The Zymomonas mobilis gene sacB that encodes the extracellular levansu crase was cloned and expressed in Escherichia coli. The gene product e xhibited both sucrose hydrolysis activity and levan forming capability . Sub-cellular fractionation of E. coli carrying pLSS41 revealed that about 95% of the total sucrase activity was detected in the cytoplasmi c fraction. The levansucrase gene was overexpressed (about hundred fol d) in E. coli under T7 polymerase expression system. Nucleotide sequen ce analysis of this gene revealed an open reading frame of 1269 bp lon g coding for a protein of 423 amino acids with a molecular mass of 46. 7 KDa. The deduced amino acid sequence was identical to the N-terminal amino acids of protein A51 of Z. mobilis ZM4. Therefore, the product of sacB is levansucrase. This is the first extracellular enzyme of Z. mobilis sequenced which does not possess a signal sequence. This gene is located 198 bp upstream of sacC gene encoding for the extracellular sucrase forming a gene cluster