Tumor Protein p53 Binding Protein 1 (TP53BP1)

TP53BP1 has a predicted molecular mass of 217 kD and shows homology in its C-terminal 247 amino acids to the C terminus of the tumor suppressor protein BRCA1. TP53BP1 was present in both the cytoplasm and nucleus in some cells and only in the nucleus in others. Furthermore, there were 2 nuclear staining patterns, one homogeneous staining and the other dot staining.TP53BP1 was required for p53 accumulation, G2/M checkpoint arrest, and the intra-S-phase checkpoint in response to ionizing radiation. TP53BP1 played a partially redundant role in phosphorylation of the downstream checkpoint effector proteins BRCA1 and CHK2 but was required for the formation of BRCA1 foci in a hierarchical branched pathway for the recruitment of repair and signaling proteins to sites of DNA damage.