Regulatory protein, which plays a central role in chromosome stability, in the p53/TP53 pathway, and DNA repair. Probably acts by blocking the action of key proteins. During the mitosis, it blocks Separase/ESPL1 function, preventing the proteolysis of the cohesin complex and the subsequent segregation of the chromosomes. At the onset of anaphase, it is ubiquitinated, conducting to its destruction and to the liberation of ESPL1. Its function is however not limited to a blocking activity, since it is required to activate ESPL1. Negatively regulates the transcriptional activity and related apoptosis activity of p53/TP53. The negative regulation of p53/TP53 may explain the strong transforming capability of the protein when it is overexpressed. May also play a role in DNA repair via its interaction with Ku, possibly by connecting DNA damage-response pathways with sister chromatid separation (By similarity). Interacts with RPS10 and DNAJA1. Interacts with the caspase-like ESPL1, and prevents its protease activity probably by covering its active site. Interacts with p53/TP53 and blocks its activity probably by blocking its binding to DNA. Interacts with the Ku 70 kDa subunit of ds-DNA kinase. Interacts with PTTG1IP (By similarity). During the stages 11.5-13.5 dpc it is expressed in most tissues of the embryo. Within the telencephalon, it is exclusively expressed inside of the ventricular zone (VZ). The expression reaches its peak by 15.5 dpc and starts to decrease by 18.5 dpc, and is not detectable in the adult brains. Most of the cells expressing it were found in the lower part of the ventricular zone. The N-terminal destruction box (D-box) acts as a recognition signal for degradation via the ubiquitin-proteasome pathway. The TEK-boxes are required for 'Lys-11'-linked ubiquitination and facilitate the transfer of the first ubiquitin and ubiquitin chain nucleation. TEK-boxes may direct a catalytically competent orientation of the UBE2C/UBCH10-ubiquitin thioester with the acceptor lysine residue (By similarity). Phosphorylated at Ser-162 by CDC2 during mitosis. Phosphorylated in vitro by ds-DNA kinase. Ubiquitinated through 'Lys-11' linkage of ubiquitin moieties by the anaphase promoting complex (APC) at the onset of anaphase, conducting to its degradation. 'Lys-11'-linked ubiquitination is mediated by the E2 ligase UBE2C/UBCH10 (By similarity). Belongs to the securin family.