We have constructed B. licheniformis borne xyl-cat fusions on multi-copy plasmids and demonstrate that glucose is an inhibitor of xylose mediated induction of transcription in vivo. Gel mobility shift experiments reveal that excess glucose interferes directly with xylose induced liberation of xyl operator DNA from the complex with Xyl repressor. The anti-inducing property of glucose suggests that Xyl repressor can bind both sugars. The lack of sequence homology to xylose isomerase supports the hypothesis of independent evolution of both proteins.