ABSTRACT
This chapter discusses the principles of gene expression control as applied in transgenic systems and looks at the different regulatory elements that are available for expression construct design. It describes the inducible transcription systems allow transgene activity in cells and transgenic animals to be controlled by the application of a small molecule (an inducer) such as isopropyl-1-thio-ß-D-galactopyranoside, doxycycline, a synthetic hormone analog or an inducer of dimerization. Expression vectors are modular in nature and often contain a whole series of different elements with different functions. Transcription factors can act either positively or negatively and in most cases interact directly with the basal transcriptional apparatus, thus either stimulating or inhibiting the recruitment and activity of RNA polymerase and the other basal components. The cloning of viral regulatory elements provided the breakthrough in animal gene transfer, since transgenes could be expressed in many different host cells using a relatively small repertoire of promoters and enhancers.
