Deletional analysis of the N-terminal half of the lyn gene

The products of the viral & cellular src gene, p60v-src and p60c-src, appear to be composed of multiple functional domains. Highly conserved regions called src homology 2 and 3 (SH2 and SH3), comprising amino acid residues 88 to 250, are believed to modulate the protein-tyrosine kinase activity present in the carboxy-terminal halves of the src proteins. To explore the functions of these regions more fully, we have introduced deletion mutations within the amino-terminal half of p56lyn, a member of the src-related family of the protein tyrosine kinases. These mutant alleles were expressed under the control of the Moloney murine leukemia virus long terminal repeat in the vector plasmid pZip-neo-SV(X) to examine the biochemical and biological properties of the mutant proteins after introduction into NIH3T3 cells and WEHI-231(immature B-cell line). No mutant proteins induced transformed foci in NIH3T3 transfectants. Deletional mutant affecting residues 163 to 234 (lyn-dC) impaired kinase activity severely and residues 35 to 60 (lyn-dV), to the lesser extent. In WEHI-231 transfectants, we could also found the inhibition of kinase activity with deletions of residues 163 to 234 (lyn-dC) and 35 to 60 (lyn-dV). WEHI-231 transfectant with lyn-dC, named WE-C was induced lesser growth arrest by crosslinking membrane IgM compared with wild type (wt) WEHI-231 cells. Down Regulation of the mutant protein stimulated with anti-IgM antibodies was detected in wt WEHI-231, but not in WEHI-231 transfectants, WE-V and WE-C. We show here the effect of the mutations in the regulatory domain on the kinase activity and the biological function of the lyn gene product, p56lyn.