What techniques can be used to control protein expression?

There are various techniques that can be used to control protein expression. 

One technique is through gene silencing. RNA interference (RNAi) can be used to selectively silence or reduce the expression of target genes. 

Another method is through gene synthesis, which optimizes codon usage. Gene synthesis provides the advantage of modifying the codon bias to better align with the host organism. For example, when using E. coli, adding expression strains with rare tRNAs can effectively surmount the codon bias associated with the recombinant gene. 

Another method involves the selection of specific promoters, which influence the rate of transcription. Inducer promoters are regulatory elements in DNA sequences that control the initiation of transcription. Repressor proteins that bind to operator sequences can inhibit transcription, and is a form of negative regulation. 

The choice of media is another way to control protein expression. All necessary nutrients for cell growth must be present from the beginning and included in the growth medium. This ensures a controlled environment for the cells to express and produce the target protein. 

Lastly, temperature can also be used to control protein expression. Decreasing the expression temperature (15-25°C) enhances the solubility of recombinant proteins. Lower temperatures slow down cellular processes, reducing rates of transcription, translation, cell division, and minimizing protein aggregation. This approach also decreases the degradation of proteolytically sensitive proteins.