Promoters control the binding of RNA polymerase and transcription factors. Since the promoter region drives transcription of a target gene, it therefore determines the timing of gene expression and largely defines the amount of recombinant protein that will be produced. Many common promoters. like CMV, EF1A, and SV40 promoters, are always active and thus referred to as constitutive promoters. Others are only active under specific circumstances. In this post, we’ll discuss inducible promoters, which can be switched from an OFF to an ON state, and how you might use these in your research. Keep a look out for a future post where we’ll discuss repressible promoters.