MRE11 is a conserved multi-functional
protein that is important for maintaining genomic integrity in yeast
and mammalian cells. By database searching, we identified a
full-length candidate MRE11 on Trypanosoma brucei chromosome II. We
subsequently cloned and sequenced the corresponding gene from the
Lister 427 strain. MRE11 is a single copy gene that encodes an 83 kDa
protein of 763 amino acids. GFP-MRE11 and Ty1-MRE11 fusion proteins
localized to the nucleus of bloodstream and procyclic T. brucei.
Interestingly, Ty1-MRE11 associated, to some extent, with telomeres
of procyclic but not bloodstream forms. This association appears
cell-cycle dependent, with the highest co- localization in G1 cells.
We were able to generate an MRE11 null mutant in bloodstream forms,
indicating that it is non-essential. However, the null mutant was
impaired in homologous recombination, as evidenced by the reduced
integration efficiency of transfected DNA. A conditional null mutant,
containing a tetracycline-inducible ectopic Ty1-MRE11, exhibited
reduced growth and plating efficiency and increased sensitivity to
DNA double-strand breaks, induced by methyl methanesulphonate or
ionizing radiation, in the absence of tetracycline.