The activity of this class of promoters is modulated by chemical compounds that either turn off or turn on gene transcription. As prerequisites, the chemicals influencing promoter activity typically
- should not be naturally present in the organism where expression of the transgene is sought;
- should not be toxic;
- should affect only the expression of the gene of interest;
- should be easy to apply or removal; and
- should induce a clearly detectable expression pattern of either high or very low gene expression
for their optimal use as modulators of gene expression.
Preferably, chemically-regulated promoters should be derived from organisms distant in evolution to the organisms where its action is required. For example, promoters to be used in plants are mostly derived from organisms such as yeast, E. coli, Drosophila or mammals.
This section presents an analysis of patents disclosing some of the main chemically-inducible promoters actually used to modulate expression in plants and animals. The promoter types analyzed are grouped as follows:
- Alcohol-regulated: Syngenta has several patents and patent applications in Europe and Australia directed to a transcriptional system containing the alcohol dehydrogenase I (alcA) gene promoter and the transactivator protein AlcR. Different agricultural alcohol-based formulations are used to control the expression of a gene of interest linked to the alcA promoter.
- Tetracycline-regulated: Yale University and BASF AG have several patents and patent applications filed in the United States, Europe, Australia and Canada covering aspects of tetracycline-responsive promoter systems, which can function either to activate or repress gene expression system in the presence of tetracycline. Some of the elements of the systems include a tetracycline repressor protein (TetR), a tetracycline operator sequence (tetO) and a tetracycline transactivator fusion protein (tTA), which is the fusion of TetR and a herpes simplex virus protein 16 (VP16) activation sequence. Eukaryotic cells transformed with the promoter systems including animal cells are claimed.
- Steroid-regulated: Numerous patent and patent applications are directed to steroid-responsive promoters for the modulation of gene expression in plant and animal cells. Analysis on patents on this type of promoters includes:
- McGill University patents on promoters based on the rat glucocorticoid receptor (GR);
- Rockefeller University patents on promoters based on the human estrogen receptor (ER);
- Syngenta and Pioneer Hi-Bred patents directed to promoters based on ecdysone receptors derived from different moth species; and
- a group of patents filed by different entities covering promoters from the steroid/retinoid/thyroid receptor superfamily.
- Metal-regulated: Promoters derived from metallothionein (proteins that bind and sequester metal ions) genes from yeast, mouse and human are the subject matter of several United States patents granted to Genentech, University Patents Inc. and The University of California (Berkeley). DNA constructs having metal-regulated promoters and eukaryotic cells transformed with them are claimed.
- Pathogenesis-related (PR) proteins are induced in plants in the presence of particular exogenous chemicals in addition to being induced by pathogen infection. Salicylic acid, ethylene and benzothiadiazole (BTH) are some of the inducers of PR proteins. Promoters derived from Arabidopsis and maize PR genes are the subject matter of patents granted to Novartis and Pioneer Hi-Bred in the United States, Australia and Europe.