Regulation of D-xylose metabolism in Caulobacter crescentus by a LacI-type repressor

Biology Department, Santa Clara University, 500 El Camino Real, Santa Clara, CA 95053 (USA); Biozentrum, University of Basel, Klingelbergstrasse 70; 4054 Basel, Switzerland

^* To whom correspondence should be addressed. Email: CStephens{at}scu.edu.

	Abstract

In the oligotrophic freshwater bacterium Caulobacter crescentus, D-xylose induces expression of over 50 genes, including the xyl operon, which encodes key enzymes for xylose metabolism. The promoter (P_xylX) controlling expression of the xyl operon is widely used as a tool for inducible heterologous gene expression in C. crescentus. We show here that P_xylX and at least one other promoter in the xylose regulon (P_xylE) are controlled by the CC3065 (xylR) gene product, a LacI-type repressor. Electrophoretic gel mobility shift assays show that operator binding by XylR is greatly reduced in the presence of D-xylose. These data support a simple regulatory mechanism in which XylR obstructs xylose-inducible promoters in the absence of the sugar; the repressor is induced to release DNA upon binding D-xylose, thereby freeing the promoter for productive interaction with RNA polymerase. XylR also has an effect on glucose metabolism, as xylR mutants exhibit reduced expression of the Entner-Doudoroff operon, and are compromised in their ability to utilize glucose as sole carbon and energy source.