Expression of an Abelson murine leukemia virus-encoded protein in Escherichia coli causes extensive phosphorylation of tyrosine residues.

A segment of the Abelson murine leukemia virus (A-MuLV) genome was inserted into an Escherichia coli plasmid designed to allow the expression of the protein encoded by the viral gene. Bacteria expressing the A-MuLV-encoded protein were isolated; they had new phosphorylated proteins in which the phosphate was linked to tyrosine residues. These proteins included many that must be E. coli protein. One phosphotyrosine-containing protein of 62,000 molecular weight had reactivity with antiserum specific for authentic A-MuLV protein. The A-MuLV protein thus appears to be a tyrosine-specific protein kinase which is active in E. coli.