Gene expression in Zymomonas mobilis: promoter structure and identification of membrane anchor sequences forming functional lacZ' fusion proteins

We have described a procedure for the isolation of lacZ' fusion genes which contain anchor sequences conferring membrane association. This method was used to isolate fragments of DNA from Zymomonas mobilis which contain promoter activity and amino-terminal sequences. The sequences and transcriptional initiation sites of three of these were compared. Both Escherichia coli and Z. mobilis recognized similar regions of DNA for transcriptional initiation. Five to eight consecutive hydrophobic amino acids in the amino terminus served to anchor these hybrid proteins to the membrane in both E. coli and Z. mobilis. General features observed in the Z. mobilis fragments included partial sequence homology with the -35 region sequence of E. coli, repetitive and palindromic A + T-rich regions preceding and adjoining the -10 region, a sequence resembling the consensus sequence of E. coli in the -10 region, and a potential ribosomal-binding site (AGGA) 8 to 12 bases upstream from an in-frame start codon. The level of expression of fusion proteins was generally higher in E. coli than in Z. mobilis. This higher level of expression in E. coli may result from multiple sites of transcriptional initiation and higher plasmid copy number.