A Conserved DNA Repeat Promotes Selection of a Diverse Repertoire of Trypanosoma brucei Surface Antigens from the Genomic Archive.

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PLoS genetics, ISSN: 1553-7404, Vol: 12, Issue: 5, Page: e1005994

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10.1371/journal.pgen.1005994; 10.1371/journal.pgen.1005994.g002; 10.1371/journal.pgen.1005994.g001; 10.1371/journal.pgen.1005994.g005; 10.1371/journal.pgen.1005994.g004; 10.1371/journal.pgen.1005994.g003
PMC4858185; 4858185
Galadriel Hovel-Miner; Monica R. Mugnier; Benjamin Goldwater; George A. M. Cross; F. Nina Papavasiliou; Harmit S. Malik
Public Library of Science (PLoS); Figshare
Agricultural and Biological Sciences; Biochemistry, Genetics and Molecular Biology; Medicine; Microbiology; Genetics; Molecular Biology; Physiology; Evolutionary Biology; Ecology; Immunology; Cancer; 110309 Infectious Diseases; 59999 Environmental Sciences not elsewhere classified; 69999 Biological Sciences not elsewhere classified; 39999 Chemical Sciences not elsewhere classified; 29999 Physical Sciences not elsewhere classified; recombinatorial homology; gene conversion events; Switching VSG expression; BES; bp; Conserved DNA Repeat Promotes Selection; Trypanosoma brucei Surface Antigens; DNA recombination events; Variant Surface Glycoprotein; Chronic trypanosome infections; Genetics and Genomics; Medical Immunology; Medical Microbiology; Parasitology
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African trypanosomes are mammalian pathogens that must regularly change their protein coat to survive in the host bloodstream. Chronic trypanosome infections are potentiated by their ability to access a deep genomic repertoire of Variant Surface Glycoprotein (VSG) genes and switch from the expression of one VSG to another. Switching VSG expression is largely based in DNA recombination events that result in chromosome translocations between an acceptor site, which houses the actively transcribed VSG, and a donor gene, drawn from an archive of more than 2,000 silent VSGs. One element implicated in these duplicative gene conversion events is a DNA repeat of approximately 70 bp that is found in long regions within each BES and short iterations proximal to VSGs within the silent archive. Early observations showing that 70-bp repeats can be recombination boundaries during VSG switching led to the prediction that VSG-proximal 70-bp repeats provide recombinatorial homology. Yet, this long held assumption had not been tested and no specific function for the conserved 70-bp repeats had been demonstrated. In the present study, the 70-bp repeats were genetically manipulated under conditions that induce gene conversion. In this manner, we demonstrated that 70-bp repeats promote access to archival VSGs. Synthetic repeat DNA sequences were then employed to identify the length, sequence, and directionality of repeat regions required for this activity. In addition, manipulation of the 70-bp repeats allowed us to observe a link between VSG switching and the cell cycle that had not been appreciated. Together these data provide definitive support for the long-standing hypothesis that 70-bp repeats provide recombinatorial homology during switching. Yet, the fact that silent archival VSGs are selected under these conditions suggests the 70-bp repeats also direct DNA pairing and recombination machinery away from the closest homologs (silent BESs) and toward the rest of the archive.