InterPro domain: IPR026584

Rad9 forms a complex with Hus1 and Rad1, called 9-1-1 complex. In human, 9-1-1 binds to TopBP1 and activates the ATR-Chk1 checkpoint pathway [ 1 ]. Rad9 also shows 3'-5' exonuclease activity [ 2 ]. Besides its function in the 9-1-1 complex, Rad9 can act as a transcriptional factor, participate in immunoglobulin classswitch recombination [ 3 ]. Aberrant Rad9 expression has been associated with prostate, breast, lung, skin, thyroid, and gastric cancers [ 4 ].

This entry includes DNA damage checkpoint proteins Rad9. Rad9 is required for transient cell-cycle arrests and transcriptional induction of DNA repair in response to DNA damage [ 5 ]. It is worth noting that this entry including the mamalian Rad9, which is homologous to the fission yeast Rad9 and the budding yeast Ddc1. Members of this family do not share the sequence homology with the budding yeast Rad9.

1. Two serine phosphorylation sites in the C-terminus of Rad9 are critical for 9-1-1 binding to TopBP1 and activation of the DNA damage checkpoint response in HeLa cells. Genes Cells 17, 807-16
2. Human DNA damage checkpoint protein hRAD9 is a 3' to 5' exonuclease. J. Biol. Chem. 275, 7451-4
3. Rad9 is required for B cell proliferation and immunoglobulin class switch recombination. J. Biol. Chem. 285, 35267-73
4. Contributions of Rad9 to tumorigenesis. J. Cell. Biochem. 113, 742-51
5. The budding yeast Rad9 checkpoint protein is subjected to Mec1/Tel1-dependent hyperphosphorylation and interacts with Rad53 after DNA damage. EMBO J. 17, 5679-88