PCNA-binding protein that acts as a regulator of DNA repair during DNA replication. Following DNA damage, the interaction with PCNA is disrupted, facilitating the interaction between monoubiquitinated PCNA and the translesion DNA synthesis DNA polymerase eta (POLH) at stalled replisomes, facilitating the bypass of replication-fork-blocking lesions. Also acts as a regulator of centrosome number. Interacts (when monoubiquitinated at Lys-15 and Lys-24) with PCNA. Interacts with isoform 2/p33ING1b of ING1. Interacts with BRCA1. Following DNA damage, localizes to DNA damage sites (PubMed:21628590). Colocalizes with centrosomes in perinuclear region (PubMed:21673012). Expressed predominantly in liver, pancreas and placenta. Not detected in heart or brain. Highly expressed in a number of tumors, especially esophageal tumors, in anaplastic thyroid carcinomas, adrenocortical carcinomas, and in non-small-cell lung cancer lines. Present only during S and G2 phases of the cell cycle. Peaks at the G2/M phase of the cell cycle and drops rapidly at mitotic exit in an APC/C-dependent manner (at protein level). By UV irradiation. By ATF3 in response to UV-stress. The PIP-box mediates the interaction with PCNA (PubMed:21628590, PubMed:23000965). The KEN box is required for the association with the APC/C complex. The D-box (destruction box) mediates the interaction with APC/C proteins, and acts as a recognition signal for degradation via the ubiquitin-proteasome pathway. The initiation motif is required for efficient chain initiation by the APC/C complex E2 ligase UBE2C. It determines the rate of substrate's degradation without affecting its affinity for the APC/C, a mechanism used by the APC/C to control the timing of substrate proteolysis during the cell cycle (PubMed:21700221). Monoubiquitinated at Lys-15 and Lys-24 during normal S phase, promoting its association with PCNA. Also diubiquitinated at these 2 sites. Following DNA damage, monoubiquitin chains at Lys-15 and Lys-24 are probably extended, leading to disrupt the interaction with PCNA. Polyubiquitinated by the APC/C complex at the mitotic exit, leading to its degradation by the proteasome. Overexpression in adrenocortical neoplasms (ACC), may promote growth and invasion in adrenal cancer. Extended N-terminus.