Transcriptional analysis of levU operon encoding saccharolytic enzymes andtwo apparent genes involved in amino acid biosynthesis in Zymomonas mobilis

Extracellular levansucrase (LevU) and sucrase (InvB) are two of the three s accharolytic enzymes involved in the sucrose metabolism of Zymomonas mobili s. The levU and invB genes were clustered with a 155 bp interval on the chr omosome. Both genes were transcribed constitutively at the basal level and the transcription of both genes was induced significantly when sucrose was added to the medium. These genes were transcribed as a bicistronic mRNA and the expression was modulated by a single promoter, which is located upstre am of the levU gene. The transcriptional initiation site was mapped to -64b p from the translation start site of levU gene. These results indicated tha t two genes are most likely to constitute an operon. The glk operon, which encodes four glycolytic enzymes, was located close to the levU operon on th e chromosome. Two apparent ORFs (ORF3 and 4) were found at the intervening sequence located between the gac and levU operons. These ORFs were transcri bed divergently and showed high homology at the amino acid level with the b acterial global regulatory protein (Lrp) and aspartate racemase. (C) 1999 E lsevier Science B.V. All rights reserved.