title: Human DNA damage checkpoint protein hRAD9 is a 3' to 5' exonuclease.
abstract: Human RAD9 protein (hRAD9) is a homolog of the fission yeast Rad9 protein, one of the six so-called checkpoint Rad proteins involved in the early steps of DNA damage checkpoint response in Schizosaccharomyces pombe. It has been shown previously that, in vivo, a highly modified form of hRAD9 makes a ternary complex with two other checkpoint Rad proteins, hRAD1 and hHUS1 (Volkmer, E., and Karnitz, L. M. (1999) J. Biol. Chem. 274, 567-570; St. Onge, R. P., Udell, C. M., Casselman, R., and Davey, S. (1999) Mol. Biol. Cell. 10, 1985-1995). However, the function of this complex is not known at present. To help define the functions of checkpoint Rad proteins in humans, we expressed hRAD9 in Escherichia coli, purified the recombinant protein and characterized it. We found that hRAD9 is a 3' to 5' exonuclease and located the nuclease active site to the region between residues 51 and 91 of the 391-amino acid-long protein. Our results suggest that exonucleolytic processing of primary DNA lesion by hRAD9 may contribute to DNA damage checkpoint response in humans.
authors.affiliation: Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599, USA.
authors.forename: T
authors.initials: T
authors.lastname: Bessho
authors.forename: A
authors.initials: A
authors.lastname: Sancar
mesh_terms: D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000201:enzymology; D004260:DNA Repair; D043211:Exodeoxyribonuclease V; D005090:Exodeoxyribonucleases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D013379:Substrate Specificity
chemical_list: D018797:Cell Cycle Proteins; D009687:Nuclear Proteins; D011994:Recombinant Proteins; C069930:rad9 protein; D005090:Exodeoxyribonucleases; D043211:Exodeoxyribonuclease V