| Abstract: | A segment of the coding sequence of the Abelson murine leukemia virus transforming gene (v-abl) has been inserted into a plasmid vector that allows its efficient and regulated expression in Escherichia coli. The product of the v-abl-derived coding sequence, designated p60v-abl, accumulated to a level of approximately 10% of total E. coli protein. A procedure is described for the isolation of p60v-abl from E. coli that yields about 50 micrograms of p60v-abl/g wet weight of E. coli. p60v-abl was capable of autophosphorylation and phosphorylating certain E. coli proteins specifically at tyrosine residues. The E. coli-expressed p60v-abl specifically phosphorylated tyrosine residues on casein and angiotensin II. The Km and Vmax values for ATP, casein, and angiotensin II in the p60v-abl kinase reaction have been determined and compared to values reported for other tyrosine-specific kinases. The expression system and isolation procedure described here permit the preparation of functional p60v-abl in quantities sufficient for detailed physical and biochemical characterization and examination of its biological action(s). |
