The human Lasp-1 (LIM and SH3 protein) gene was previously identified by differential screening of a breast cancer-derived metastatic lymph node cDNA library. It was located on the q12-q21 region of human chromosome 17 and was shown to be amplified and overexpressed in 12% of breast tumors. Lasp-1 defines a new LIM-protein subfamily, as it associates a C-terminal Src homology 3 (SH3) domain to a N-terminal LIM motif. In this study, the isolation and characterization of the cDNA encoding the mouse Lasp-1 protein are described, and it is shown to be highly conserved with its human counterpart. In addition to the LIM and SH3 domains, both human and mouse Lasp-1 contain an actin-binding domain. The mouse gene was mapped by in situ hybridization to the 11C-11D region of chromosome 11. Northern blot analysis shows that this gene is expressed from 7.5 to 17.5 days post-coitum of mouse embryogenesis and in almost all adult tissues.