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Regulation of D-Xylose Metabolism in Caulobacter crescentus by a LacI-Type Repressor

Craig Stephens,^1* Beat Christen,^2, Kelly Watanabe,¹ Thomas Fuchs,^2, and Urs Jenal²

Biology Department, Santa Clara University, 500 El Camino Real, Santa Clara, California 95053,¹ Biozentrum, University of Basel, Klingelbergstrasse 70, 4054 Basel, Switzerland²

Received 17 August 2007/ Accepted 29 September 2007

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 showed that operator binding by XylR is greatly reduced in the presence of D-xylose. The data support the hypothesis that there is 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 their ability to utilize glucose as a sole carbon and energy source is compromised.

Published ahead of print on 12 October 2007.

Present address: Department of Development Biology, Stanford University School of Medicine, Stanford, CA 943005.

Present address: Synthes Biomaterials, Guterstrasse 5, 2544 Bettlach, Switzerland.