Rad21 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. Rad21 protein is a nuclear phospho-protein, which becomes hyperphosphorylated in cell cycle M phase. Rad21 plays a crucial role in the cohesin complex, which is essential for proper segregation of sister chromatids during cell division. By holding sister chromatids together until anaphase, Rad21 ensures accurate chromosomal separation, thereby maintaining genomic stability. Additionally, Rad21 is involved in the repair of double-strand breaks in DNA, making Rad21 vital for cellular responses to DNA damage and mitotic growth. Notably, Rad21 undergoes C-terminal cleavage in response to various stimuli prior to apoptosis, resulting in a cleavage product that translocates to the cytoplasm and participates in early apoptotic events, amplifying the cell death signal through a positive-feedback mechanism.