Overproduction in Escherichia coli, purification and properties of human prothymosin alpha

A bacterial strain overproducing human prothymosin alpha was constructed based on the efficient T7 RNA polymerase transcription of human prothymosin alpha cDNA. The highest yield of the human prothymosin alpha, up to 30% of the total bacterial protein, was achieved with constructions containing 6-10 nucleotides between the Shine-Dalgarno sequence and initiation ATG codon. Unexpectedly, cells grown in the presence of inducer of T7 RNA polymerase synthesis produced substantially lower levels of prothymosin alpha than those grown in the absence of inducer. A simple procedure for prothymosin alpha isolation was elaborated, resulting in large amounts of electrophoretically pure and immunoactive protein.