 Rad9 is activated by multiple phosphorylations by cyclin dependent kinases and activates Rad53 through Mec1 downstream.Mrc1 has also been shown to work cooperatively to recruit Rad53 to damaged DNA.After the 9-1-1 complex Rad9 is extensively phosphorylated by Mec1 which can trigger self-association of more Rad9 oligomers on the chromosomes.