iASPP (inhibitor of apoptosis stimulating protein of p53, RelA-associated inhibitor (RAI), NFKap B-interacting protein 1, protein phosphatase 1 regulatory subunit 13-like, PPP1R13L) is the third member of the ASPP family of proteins. Unlike ASPP1 and ASPP2, which interact with p53 and enhance its ability to induce apoptosis, iASPP inhibits apoptosis induced by p53 overexpression. iASPP has been identified in a yeast-two hybrid screen as an interacting protein of the p65 subunit of NFKap B (RelA),3 interacts with NFKap B in vivo, and acts as an efficient inhibitor of HIV-1 gene expression in which both NFKap b and Sp1 play major roles. iASPP expression is upregulated in human breast carcinomas expressing wild-type p53, and gene overexpression may play an important role in the leukemogenesis and/or progression of acute leukemia. Alternate Names: apoptosis stimulating protein of P53 1; Apoptosis-stimulating of p53 protein 2; Tumor suppressor p53-binding protein 2; p53-binding protein 2; p53BP2; 53BP2; Bcl2-binding protein; Bbp; Renal carcinoma antigen NY-REN-51.