TITLE:
Regulation of D-galacturonate metabolism in Caulobacter crescentus by HumR, a LacI-family transcriptional repressor
AUTHORS:
Aaesha I. Sheikh, Deborah Caswell, Cynthia Dick, Spencer Gang, Justin Jarrell, Ankita Kohli, Amanda Lieu, Jared Lumpe, Meghan Garrett, Jennifer Parker, Craig Stephens
KEYWORDS:
Caulobacter; Galacturonate; LacI
JOURNAL NAME:
Advances in Bioscience and Biotechnology,
Vol.4 No.10B,
October
8,
2013
ABSTRACT:
The oligotrophic freshwater bacterium Caulobacter crescentus encodes a cluster
of genes (CC_1487 to CC_1495) shown here to be necessary for metabolism of
D-galacturonate, the primary constituent of pectin, a major plant polymer.
Sequence analysis suggests that these genes encode a version of the bacterial
hexuronate isomerase pathway. A conserved 14 bp sequence motif is
associated with promoter regions of three operons within this cluster, and is
conserved in homologous gene clusters in related alpha-Proteobacteria.
Embedded in the hexuronate gene cluster is a gene (CC_1489) encoding a member
of the LacI family of bacterial transcription factors. This gene product,
designated here as HumR (hexuronate metabolism regulator),
represses expression of the uxaA and uxaC operon promoters by binding to the
conserved operator sequence. Repression is relieved in the presence of
galacturonate or, to a lesser extent, by glucuronate. Other genes potentially
involved in pectin degradation and hexuronate transport are also under the
control of HumR. Adoption of a LacI-type repressor to control hexuronate
metabolism parallels the regulation of xylose, glucose, and maltose utilization
in C. crescentus, but is distinct from
the use of GntR-type repressors to control pectin and hexuronate utilization
in gamma-Proteobacteria such as Escherichia
coli.