Two nucleotide sequences coding for mature human immune interferon (IFN-γ) and differing from each other by nine N-terminal nucleotides were expressed in E. coli under the control of a trp promoter. The longer gene variant after the ATG initiatory codon contained a TGT TAC TGC sequence, which was absent in the shorter gene. When expressed in E. coli under the direction of identical transcription and translation regulatory elements, these genes showed different susceptibility to induction. © 1987.