Nucleic Acids Research Advance Access originally published online on May 3, 2007
Nucleic Acids Research 2007 35(10):3478-3493; doi:10.1093/nar/gkm249
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Nucleic Acids Research, 2007, Vol. 35, No. 10 3478-3493
© 2007 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Molecular Biology |
Trypanosoma brucei homologous recombination is dependent on substrate length and homology, though displays a differential dependence on mismatch repair as substrate length decreases
The Wellcome Centre for Molecular Parasitology,University of Glasgow,Glasgow Biomedical Research Centre,120 University Place,Glasgow,G12 8TA, UK
*To whom correspondence should be addressed. Tel: 0044 141 330 5946; Fax: 0044 141 330 5422; Email: rmc9z{at}udcf.gla.ac.uk
Received March 14, 2007. Revised April 4, 2007. Accepted April 5, 2007.
Homologous recombination functions universally in the maintenance of genome stability through the repair of DNA breaks and in ensuring the completion of replication. In some organisms, homologous recombination can perform more specific functions. One example of this is in antigenic variation, a widely conserved mechanism for the evasion of host immunity. Trypanosoma brucei, the causative agent of sleeping sickness in Africa, undergoes antigenic variation by periodic changes in its variant surface glycoprotein (VSG) coat. VSG switches involve the activation of VSG genes, from an enormous silent archive, by recombination into specialized expression sites. These reactions involve homologous recombination, though they are characterized by an unusually high rate of switching and by atypical substrate requirements. Here, we have examined the substrate parameters of T. brucei homologous recombination. We show, first, that the reaction is strictly dependent on substrate length and that it is impeded by base mismatches, features shared by homologous recombination in all organisms characterized. Second, we identify a pathway of homologous recombination that acts preferentially on short substrates and is impeded to a lesser extent by base mismatches and the mismatch repair machinery. Finally, we show that mismatches during T. brucei recombination may be repaired by short-patch mismatch repair.
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