A new member of the human src gene family was isolated on the basis of cross hybridization with the probe v-fgr. Cloning and sequencing the cDNAs showed that the new gene, termed c-slk, encodes 537 amino acid proteins whcih have extensive homology with other src tyrosine kinase genes but an essentially nonhomologous N-terminal segment of 82 amino acids. The chimeric construct, which has the Gardner-Rasheed feline sarcoma virus (GR-FeSV) sequence 5' half and c-slk tyrosine kinase domain at 3' half, transformed the mouse fibroblast NIH/3T3. The transformed cells had the chimeric phosphoprotein p71 gag/slk which has been tyrosine kinase in vitro. For the purpose of pursuing the possible involvement of c-slk in human tumorigenesis, the c-slk gene was localized on the long arm of chromosome 6. We are now screening various human tumor DNAs in terms of rearrangements and amplification of c-slk.