The p53 binding protein 2 (53BP2) has been initially identified as an interacting protein to p53 and subsequent studies have shown that it also interacts with Bcl-2 and NF-kappaB p65 subunit. We have previously found that the TP53BP2 gene encoding 53BP2 protein is a single copy gene and has been mapped to the long arm of chromosome I at q42. 1. The subsequent studies revealed that TP53BP2 encodes two proteins, 53BP2 and ASPP2, of 1005 and 1128 amino acids, respectively. ASPP2 contains additional 123 amino acids to the N-terminus of 53BP2. In this study, we have examined the genomic organization of TP53BP2 transcripts and found that it encodes two mRNA species, either with (53BP2) or without exon 3 (ASPP2), by alternative splicing in various cell lines and tissues. Thus, we propose to call these proteins as 53BP2S (short) and 53BP2L (long), respectively. (C) 2004 Elsevier Inc. All rights reserved.