Many different tools exist to affect heterologous gene expression.
These tools include such things as changing gene copy number, changing promoter strength, using regulatable and finely tunable promoters, and optimizing untranslated regions and codon usage for transcript stability and translational efficiency. One of the more recently developed tools includes the ability to affect and coordinated multiple gene expression by directing the processing and stabilities of novel operons. The power of these methods will be not only in developing them as individual tools, but using them in combination on desired systems. An expression system was developed that allowed for the easy introduction of mRNA stability control elements into various regions of a dual-gene operon through DNA cassettes. The affects imparted by only changing DNA copy number were a function of inducer concentration, the combination of mRNA stability control elements used, and the particular gene.