Escherichia coli BL21 (DE3) co-transformed with the gene of human interferon-alpha 2a (IFN-alpha 2a) and the argU gene that codes for minor tRNA(Arg(AGG/AGA)) produced IFN-alpha 2a in yield of more than 25% of the total cellular proteins. IFN-alpha 2a was purified from insoluble inclusion bodies as much as 10 mg per liter of LB culture and the methionine residue at the N-terminus was found to be completely processed.