Effect of amino acid substitutions in the rad50 ATP binding domain on DNA double strand break repair in yeast.

Department of Molecular Medicine, Institute of Biotechnology, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78245, USA.
The Saccharomyces cerevisiae Rad50-Mre11-Xrs2 complex plays a central role in the cellular response to DNA double strand breaks. Rad50 has a globular ATPase head domain with a long coiled-coil tail. DNA binding by Rad50 is ATP-dependent and the Rad50-Mre11-Xrs2 complex possesses DNA unwinding and endonuclease activities that are regulated by ATP. Here we have examined the role of the Rad50 Walker type A ATP binding motif in DNA double strand break repair by a combination of genetic and biochemical approaches. Replacement of the conserved lysine residue within the Walker A motif with alanine, glutamate, or arginine results in the same DNA damage sensitivity and homologous recombination defect as the rad50 deletion mutation. The Walker A mutations also cause a deficiency in non-homologous end-joining. As expected, complexes containing the rad50 Walker A mutant proteins are defective in ATPase, ATP-dependent DNA unwinding, and ATP-stimulated endonuclease activities. Although the DNA end-bridging activity of the Rad50-Mre11-Xrs2 complex is ATP-independent, the end-bridging activity of complexes containing the rad50 Walker A mutant proteins is salt-sensitive. These results provide a molecular explanation for the observed in vivo defects of the rad50 Walker mutant strains and reveal a novel ATP-independent function for Rad50 in DNA end-bridging.
Mesh Terms:
Adenosine Triphosphatases, Adenosine Triphosphate, Alanine, Amino Acid Motifs, Arginine, DNA, DNA Damage, DNA Repair, DNA-Binding Proteins, Dose-Response Relationship, Radiation, Endonucleases, Gamma Rays, Genetic Complementation Test, Glutamic Acid, Lysine, Mutation, Plasmids, Protein Binding, Protein Structure, Tertiary, Recombination, Genetic, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins, Time Factors
J. Biol. Chem. Jan. 28, 2005; 280(4);2620-7 [PUBMED:15546877]
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