 From this they suspected that "Rad9" is necessary to invoke G2 cell cycle arrest.To confirm this they tested a double mutant of "rad9" with DNA repair deficient-strain "rad52" and found that the cell failed to arrest in G2 further proving that a functioning Rad9 gene is needed to induce G2 arrest.They then used MBC, a microtubule inhibitor, to synthetically arrest the cell in G2 in order to test if the "Rad9" gene was necessary to also repair DNA.