RAD21, also named as Nuclear matrix protein 1, is a 631 amino acid protein, which belongs to the rad21 family. The calculated molecular weight of RAD21 is 72 kDa, but the phosphorylated RAD21 is about 120 kDa. The protein encoded by this gene is highly similar to the gene product of Schizosaccharomyces pombe rad21, a gene involved in the repair of DNA double-strand breaks, as well as in chromatid cohesion during mitosis. This protein is a nuclear phospho-protein, which becomes hyperphosphorylated in cell cycle M phase. The highly regulated association of this protein with mitotic chromatin specifically at the centromere region suggests its role in sister chromatid cohesion in mitotic cells