This protein domain family is the C-terminal domain of PAXIP1-associated-protein-1, which also goes by the name PTIP-associated protein 1. This family of proteins is found in eukaryotes. The function of this protein is to localise at the site of DNA damage and form foci with PTIP at the DNA break point. Furthermore, studies have shown that depletion of PA1 increases cellular sensitivity to ionizing radiation. Proteins in this family are typically between 122 and 254 amino acids in length [1].

1: Accumulation of Pax2 transactivation domain interaction protein (PTIP) at sites of DNA breaks via RNF8-dependent pathway is required for cell survival after DNA damage. Gong Z, Cho YW, Kim JE, Ge K, Chen J; J Biol Chem. 2009;284:7284-7293. PMID:19124460