Reconstitution and molecular analysis of the hRad9-hHus1-hRad1 (9-1-1) DNA damage responsive checkpoint complex.
DNA damage activates cell cycle checkpoint signaling pathways that coordinate cell cycle arrest and DNA repair. Three of the proteins involved in checkpoint signaling, Rad1, Hus1, and Rad9, have been shown to interact by immunoprecipitation and yeast two-hybrid studies. However, it is not known how these proteins interact and assemble into a complex. In the present study we demonstrated that in human cells all the hRad9 and hHus1 and approximately one-half of the cellular pool of hRad1 interacted as a stable, biochemically discrete complex, with an apparent molecular mass of 160 kDa. This complex was reconstituted by co-expression of all three recombinant proteins in a heterologous system, and the reconstituted complex exhibited identical chromatographic behavior as the endogenous complex. Interaction studies using differentially tagged proteins demonstrated that the proteins did not self-multimerize. Rather, each protein had a binding site for the other two partners, with the N terminus of hRad9 interacting with hRad1, the N terminus of hRad1 interacting with hHus1, and the N terminus of hHus1 interacting with the C terminus of hRad9's predicted PCNA-like region. Collectively, these analyses suggest a model of how these three proteins assemble to form a functional checkpoint complex, which we dubbed the 9-1-1 complex.
Burtelow
M A
MA
Division of Developmental Oncology Research, Department of Molecular Pharmacology, Mayo Clinic, Rochester, Minnesota 55905, USA.
Roos-Mattjus
P M
PM
Rauen
M
M
Babendure
J R
JR
Karnitz
L M
LM
D002453:Cell Cycle / Q000235:genetics; D018797:Cell Cycle Proteins / Q000235:genetics; D004249:DNA Damage; D004260:DNA Repair / Q000235:genetics; D004268:DNA-Binding Proteins; D004720:Endonucleases / Q000235:genetics; D005786:Gene Expression Regulation; D018816:Genes, cdc; D006801:Humans; D020014:K562 Cells; D029702:Schizosaccharomyces pombe Proteins
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D029702:Schizosaccharomyces pombe Proteins; C106332:hus1 protein, S pombe; C069930:rad9 protein; D004720:Endonucleases