Abstract: DNA sequences, recombinant DNA molecules and hosts transformed with them which produce polypeptides displaying a biological or immunological activity of gamma interferon. The genes coding for these polypeptides and methods of making and using these DNA sequences, molecules, hosts, genes and polypeptides are disclosed. The DNA sequences of this invention are further characterized by expression control sequences which permit the production of gamma interferon in high yields. More particularly, these expression control sequences comprise the .lambda. P.sub.L promoter, and more preferably, a trp-derived expression control sequence containing the sequence ATCGATACT between the Shine-Dalgarno sequence and the translational start signal.