CCNA2/CDK2 regulatory protein that transiently maintains CCNA2 in the cytoplasm. Interacts with CCNA2/CDK2 complex, but not with CCNA2/CDC2, CCNB1/CDC2 or CCNE1/CDK2 complexes, at multiple phases of the cell cycle, including S and G2/M. Predominantly located in the endoplasmic reticulum, only a small portion is detected in the nucleus. Widely expressed with high expression in testis. Isoform 1 is detected in various tissues, including retina, fetal and adult brain. Isoform 2 is expressed in the retina at high levels, and in the brain at very low levels (PubMed:28794130). Expressed at each stage of the cell cycle, including G0, although the expression is somewhat higher in late G1 and S phases. Phosphorylated in vitro by the CCNA2/CDK2 complex. The disease may be caused by variants affecting the gene represented in this entry. Truncated N-terminus. Truncated N-terminus. Contaminating sequence. Potential poly-A sequence. Truncated N-terminus. Probable cloning artifact.