Recently, we cloned a cDNA encoding a novel mouse protein. named A-Cl. by differential display between two mouse cell lines, embryonic fibroblast C3H10TI/2 and chondrogenic ATDC5. Mouse A-Cl has homology with a ras-responsive gene, rat Ha-rev107 (Hrasls), and modulates a Ha-ras-mediated signaling pathway. Here, we report a cDNA encoding a human homolog of mouse A-Cl. The deduced amino acid sequence of human A-Cl consists of 168 amino acids, and shows 83% identity with that of mouse A-Cl. Human A-Cl mRNA was expressed in skeletal muscle, testis, heart, brain, and thyroid in vivo. Moreover, expression of human A-Cl mRNA was detected at a high level in human osteosarcoma-derived U2OS cells in vitro. By FISH analysis the human A-Cl gene (HRASLS) was mapped to human chromosome 3q28 --> q29. Copyright (C) 2001 S. Karger AG, Basel.