Interferon gamma is a molecule which may serve as a good object for studying and explaining the role of expression limiting conditions. Three levels of limiting factors modifications, i. e. operon choice and structure, changes in the secondary mRNA structure, and the influence of post-translational modulation processes are described. The relationship between the operon stucture and expression level for other heterologous proteins is compared with that of IFN-gamma. In particular, the shape of ribosome binding site (RBS) region and its affected different nucleotide substitutions are presented. The rule of N-terminal and C-terminal end changes for protein stability and inclusion body formation is also shown.