Regulation of xylose utilization in Bacillus licheniformis: Xyl repressor-xyl-operator interaction studied by DNA...

Xylose utilization in Bacillus licheniformis is inducible by xylose. We establish here that the Xyl repressor recognizes and binds an xyl operator sequence located 12 nucleotides downstream from the transcription start site of the xyl operon. DNA-retardation experiments employing xyl regulatory DNA and soluble protein extracts indicate complex formation in the presence of Xyl repressor. Two repressor-operator complexes are distinguished by different gel mobilities. They yield the same in situ copper-phenanthroline footprint. This result suggests that a single xyl operator may be bound by different oligomers of Xyl repressor. Methylation and hydroxyl radical cleavage protection of the xyl operator by Xyl repressor binding and ethylation interference of Xyl repressor binding to the xyl operator reveals symmetrical interaction of the repressor with two half sites of the operator, which show palindromic symmetry and are located on the same side of the B-form DNA structure.