Microbiology news and views
J. Mol. Micro. Biotechnol. 3: 113-122
Organisation and Evolution of the tol-pal Gene Cluster
James N. Sturgis
The genomic context and phylogenetic distribution of the
tol-pal gene cluster and homologues to its various components have been investigated. The structure of
this operon is well conserved across the Gram negative bacteria, and the machine encoded by these genes probably evolved with the appearance of Gram
negative bacteria. Since the evolutionary appearance of the operon some species appear to have lost the genes. These bacteria seem to fall into two classes, namely
obligate intracellular parasites and bacteria that produce large numbers of outer membrane vesicles. The evolution of the
ab and g proteobacteria was accompanied by the association of an additional gene
(ybgC) with the operon. Several coincidences of genomic context argue for an important role of the
tol-pal operon in cell envelope maintenance. Genes homologous to
tolQ and tolR proved to be very widespread being found throughout the eubacteria, and one example in the archea, this
distribution argues for an ancient origin of these genes. The genomic context of these genes often suggests a role in micro-nutrient uptake. Interestingly in all the cases
examined the tolQ and tolR genes or their homologues appear to be present as a pair, with a potential for a tight translational regulation.
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