The murine cell surface antigen ADAM 15 is a transmembrane glycoprotein that is expressed in a variety of cells including monocytic and T cell lines and consists of a metalloprotease domain, a disintegrin domain, a cysteine-rich domain, and an epidermal growth factor (EGF)-like domain in the extracellular region. The cytoplasmic domain comprises 103 amino acids containing proline-rich endophilin I, Src homology 3 (SH3), and phox homology domain-containing protein (SH3PX1) binding motifs. The ADAM15 gene is composed of 21 exons and 20 introns and spans approximately 10 kb. The transcription initiation site of the ADAM15 gene was defined by an oligonucleotide-capping method. Reverse transcription (RT)-PCR using primers of the cytoplasmic domain of ADAM15 revealed the presence of different ADAM15 species designated ADAM15v1 and ADAM15v2, respectively, that had characteristic SH3-binding class I and/or class II motifs. The ADAM15v1 and ADAM15v2 genes consist of an extra one exon and two exons, respectively, which exist in intron 19 of the ADAM15 gene. The expression of ADAM15v1 and ADAM15v2 mRNA was found in T lymphocyte and monocyte lines. ADAM15v2 protein interacted more strongly with the Src family proteins Lck and Src than ADAM15 protein, when examined by pull-down and immunoprecipitation followed by immunoblot analysis using a T lymphocyte line. Phosphorylation of ADAM15v2 protein markedly enhanced the binding with Lck. These results suggest that the cytoplasmic domain of ADAM15v2 strongly interacts with Lck and plays an important role in T lymphocytes.