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Description

PAX-interacting protein 1 (UniProt: Q6NZQ4, also known as PAX transactivation activation domain-interacting protein, PAXIP1) is encoded by the Paxip1 (also known as Ptip) gene (Gene ID: 55982) in murine species. PAXIP1 is a nuclear matrix protein that is involved in DNA damage response and in transcriptional regulation through histone methyltransferase (HMT) complexes such as the MLL2/MLL3 complex. In vitro it is shown to be involved in the homologous recombination mechanism for the repair of double-strand breaks. It recruits Tp53bp1 to DNA damage foci and effective DNA damage response appears to require the association with Tp53bp1 phosphorylated by ATM. It also recruits PAGR1A (Pax-Interacting Protein 1-associated glutamate rich protein 1a) to DNA damage sites and PAGR1A:PAXIP1 complex is believed to be essential for cell survival. PAXIP1 expression is reported in all tissues and high expression is observed in embryonic kidney and brain. PAXIP1 contains 6 BRCT domains and BRCT domains 1 and 2 mediate its interaction with PAGR1A and interaction with MLL2/MLL3 is accomplished with BRCT domains 5 and 6. Mice with defective Paxip1 gene are developmentally retarded and usually face embryonic lethality by day 9.5 (E9.5).