PA1 (PTIP-associated protein 1) was isolated as a protein that associates with PTIP (Pax transactivation domain-interacting protein), a nuclear protein involved in the DNA damage response and interacts with the Pax2 transactivation domain. Along with PTIP, PA1 has been found to be present in a MLL3- and MLL4-containing Histone H3 Lysine 4 Methyltransferase complex. PA1 also appears to be important to the DNA damage response and repair. This involvement in DNA damage signaling is reported to be independent of its MLL association. PA1 has also been identified as GAS (glutamate-rich coactivator interacting with SRC1/NCOA1). As an interactor of SRC1 (steroid receptor coactivator 1), PA1 functions as a transcription cofactor.