Ionizing radiation can interact with DNA and induce numerous types of lesions within DNA.The studies on irradiated cells determined that effective triggering of S-phase arrest in response to ionizing radiation gives rise to the radioresistant DNA synthesis phenotype.SMC1 protein, a chromosomal protein member of the cohesin complex that enables sister chromatid cohesion and plays a role in DNA repair, is required for activation of intra-S-phase checkpoint.