Selective cloning of Bacillus subtilis xylose isomerase and xylulokinase in Escherichia coli genes by IS5-mediated expression.

A fragment of Bacillus subtilis DNA coding for xylose isomerase and xylulokinase was isolated from a BamHI restriction pool by complementation of an isomerase-defective Escherichia coli strain. The spontaneous insertion of IS5, which occurred during the very slow growth of the E. coli xyl- cells on xylose, allowed the expression of the cloned Bacillus genes in E. coli. Without IS5 insertion, the xylose genes were inactive in E. coli. Deletion experiments indicated that the control of the expression resides within a 270-bp long region at the right end of IS5. Deletion of this region led to a loss of expression, which could be restored by insertion of the lacUV5 promoter fragment at the deletion site. Sequence analysis showed that the site of IS5 insertion is 195 bp upstream from the putative ATG initiation codon of the xylose isomerase structural gene. This ATG is preceded by a ribosome binding sequence and two hexamers also found in promoter regions of other Bacillus genes. Deletion and mutagenesis analysis led to a preliminary map of the Bacillus xylose operon.