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Three c-yes cDNA clones were obtained from poly(A)+ RNA of human embryo fibroblasts. Sequence analysis of the clones showed that they contained inserts corresponding to nearly full-length human c-yes mRNA, which could encode a polypeptide of 543 amino acids with a relative molecular weight (Mr) of 60,801. The predicted amino acid sequence of the protein has no apparent membrane-spanning region or suspected ligand binding domain and closely resembles pp60c-src. Comparison of the sequences of c-yes and v-yes revealed that the v-yes gene contains most of the c-yes coding sequence except the region encoding its extreme carboxyl terminus. The region missing from the v-yes protein is the part that is highly conserved in cellular gene products of the protein-tyrosine kinase family.

With v-yes DNA as the probe, a human cDNA library made from placental RNA was screened under relaxed conditions, and DNA clones derived from a novel genetic locus, termed lyn, were obtained. Nucleotide sequencing revealed that lyn could encode a novel tyrosine kinase that was very similar to mouse T-lymphocyte-specific tyrosine kinase p56lck and the v-yes protein as well as to the gene products of v-fgr and v-src. Northern hybridization analysis revealed that a 3.2-kilobase lyn mRNA was expressed in a variety of tissues of the human fetus. The pattern of lyn mRNA expression was different from those of related genes, such as yes and syn. Hybridization analysis of DNA from sorted chromosomes showed that the lyn gene is located on human chromosome 8 q13-qter.