Efficient production of human gamma interferon in tobacco protoplasts by genetically engineered brome mosaic virus RNAs.

We succeeded in producing human gamma interferon (IFN-gamma) in tobacco protoplasts in quantity using genetically engineered brome mosaic virus (BMV strain ATCC66). This strain of BMV produces two types of coat protein, a full-length coat protein (20K) and a truncated coat protein (19K) which are translated from the first and second initiation codons, respectively. We replaced the truncated coat protein gene with the IFN-gamma gene and synthesized BMV-IFN-gamma chimera RNAs using an in vitro transcription system. The BMV-IFN-gamma chimera RNAs were used to inoculate tobacco protoplasts together with BMV RNA 1 and RNA 2 and produced IFN-gamma to a level of 5 to 10% of total extracted proteins per infected protoplast after 24 h of incubation. The efficient production of IFN-gamma was attributed to the high translation activity of the BMV-IFN-gamma chimera RNA. We demonstrate that 24 nucleotides coding for the N-terminal amino acids of the full-length coat protein were probably involved in the high translation activity of the BMV-IFN-gamma chimera RNA.