Mre11
nuclease activity is required for the repair of topoisomerase II mediated DNA
damage.
John Nitiss,
Alexandre Stepanov, Karin Nitiss
Molecular Pharmacology, St. Jude Children's Res. Hosp., 332 N. Lauderdale,
Memphis, TN 38015, USA (john.nitiss@stjude.org)
Top2p carries out topological changes in DNA by introducing a transient DNA double strand break, forming 5' phosphotyrosine covalent complexes with DNA. This property of the enzyme reaction has been exploited by therapeutic agents, which trap Top2p at this point in the reaction cycle. Repair of Top2p mediated DNA damage requires double strand break (DSB) repair and other functions to remove covalently bound protein. Nash has identified Tdp1, which can remove Top1p, but not Top2p covalently bound to DNA. A candidate for removal of Top2p is the Mre11 complex, which is required for the removal of Spo11p; a Top2p related protein that generates DSBs to initiate meiotic recombination. mre11 mutants that are competent at DSB repair, but which fail to remove Spo11p in meiosis have been described. These mutants confer hypersensitivity to drugs targeting Top2p but do not affect sensitivity to the Top1 drug camptothecin. Sae2 is required for Mre11 nuclease activity. Like mre11 nuclease- mutants, sae2 deletion mutants can carry out DSB repair, but cannot remove Spo11p. sae2 mutants are hypersensitive to Top2p targeting drugs, but have wild type sensitivity to camptothecin. Taken together, our results show a requirement for the Mre11 complex in the repair of Top2 mediated DNA lesions, a role that appears separate from the requirement for Mre11 in DSB repair. We suggest that MRE11 is a major protein for removing proteins such as topo II that are covalently bound to the 5' end of DNA.