Arg encodes a protein highly related to the c-abl gene product with regard to 
overall structural architecture as well as the amino acid sequences of their 
tyrosine kinase, and src-homologous 2 and 3 domains. The two genes form a 
distinct subfamily of non-receptor tyrosine kinases and share a common homolog 
in Drosophila. In this study we characterized the arg protein product by 
expression of its coding sequence in bacteria. The recombinant arg protein was 
detected in bacterial lysates by immunoblotting and exhibited a molecular mass 
of 145 kDa. Phosphoamino acid analysis of the arg gene product following an 
immune complex autokinase reaction revealed tyrosine phosphorylation and 
established that it possesses tyrosine kinase activity. High-titer antibody 
capable of detecting the cellular arg gene product was generated by expressing a 
carboxy-terminal segment of arg in bacteria and using the recombinant protein as 
an immunogen. The arg gene product was identified in cultured human cells as a 
145 kDa protein that exhibited autokinase activity. Analysis of arg expression 
in murine tissues revealed that arg, like c-abl, is widely expressed, further 
extending the similarities between the two genes, and suggesting that arg 
probably functions in signaling pathways fundamental to many cell types.