title: Integrated circuits: how transcriptional silencing and counter-silencing facilitate bacterial evolution.
abstract: Horizontal gene transfer is a major contributor to bacterial evolution and diversity. For a bacterial cell to utilize newly-acquired traits such as virulence and antibiotic resistance, new genes must be integrated into the existing regulatory circuitry to allow appropriate expression. Xenogeneic silencing of horizontally-acquired genes by H-NS or other nucleoid-associated proteins avoids adventitious expression and can be relieved by other DNA-binding counter-silencing proteins in an environmentally-responsive and physiologically-responsive manner. Biochemical and genetic analyses have recently demonstrated that counter-silencing can occur at a variety of promoter architectures, in contrast to classical transcriptional activation. Disruption of H-NS nucleoprotein filaments by DNA bending is a suggested mechanism by which silencing can be relieved. This review discusses recent advances in our understanding of the mechanisms and importance of xenogeneic silencing and counter-silencing in the successful integration of horizontally-acquired genes into regulatory networks.
authors.affiliation: Department of Laboratory Medicine, University of Washington School of Medicine, Seattle, WA 98195, USA.
authors.forename: W Ryan
authors.initials: WR
authors.lastname: Will
authors.affiliation: Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
authors.forename: William W
authors.initials: WW
authors.lastname: Navarre
authors.affiliation: Department of Laboratory Medicine, University of Washington School of Medicine, Seattle, WA 98195, USA; Department of Microbiology, University of Washington School of Medicine, Seattle, WA 98195, USA. Electronic address: fcfang@u.washington.edu.
authors.forename: Ferric C
authors.initials: FC
authors.lastname: Fang
mesh_terms: D001419:Bacteria / Q000235:genetics*; D019143:Evolution, Molecular; D015870:Gene Expression; D015964:Gene Expression Regulation, Bacterial; D053263:Gene Regulatory Networks; D020868:Gene Silencing; D022761:Gene Transfer, Horizontal