Plant Ubiquitin promoter (Ubi)
Ubiquitin is a protein found in eukaryotic cells and its sequence is highly conserved among organisms as diverse as humans and the fruit fly. The protein is implicated in processes such as protein turnover, chromatin structure, cell cycle control, DNA repair, and response to heat shock and other stresses.
In 1992, Christensen et al. identified two out of the 8 to 10 loci encoding ubiquitin in maize. Both characterized genes, Ubi-1 and Ubi-2, contain an open reading frame of 1599 bp arranged as seven tandem, head-to-tail repeats of 228 bp.
The regulatory region which controls the expression of the Ubi-1 gene of maize extends from -899 bp 5′ of the transcription start site (+1) to about 1093 bp 3′ of the transcription start site.
This sequence of approximately 2 kb comprises:
- a TATA box sequence located at -30,
- two overlapping sequences that are similar to the consensus heat shock element found in heat-inducible genes, located at the -214 and -204 position from the transcription start site,
- an 83 bp untranslated exon sequence 3′ of and adjacent to the transcription start site and
- an intron of around 1 kb, which extends from 84 to 1093 position.
The heat shock elements of the regulatory region enhance the expression of the ubiquitin protein in response to temperature stress.
Mycogen Plant Science (now owned by Dow Agro Sciences) and Monsanto PLC are entities that have patents and patent applications on the plant ubiquitin regulatory system. TheMycogen patents evaluated in this report were granted in:
- the United States (4 patents)
- Europe (1 patent), and
- Canada (1 patent)
Monsanto has granted patents in the United States and Australia. Related patent applications were also filed in Europe and Canada.
Prodigene owns a United States patent and also filed a patent application in Australia.
How is promoter defined?
The description of a eukaryotic promoter in both Mycogen patents and Monsanto patent applications includes functional and structural components. That is, a promoter is defined as the region upstream of a gene containing the binding site for RNA polymerase II that initiates transcription of the DNA. It contains a TATA box, a CAAT box or an AGGA box, and the CAP site. The inventors also acknowledge that there are ancillary regulatory sequences or regions that are part of a regulatory system in general. Those regions include enhancers and upstream activating sequences.
One of the regulatory elements set out by the inventors of the Mycogen patents is the heat shock element, which transiently enhances the level of downstream gene expression in response to sudden temperature elevation.
Thus, the inventions described in the patents do not refer to a “simple” ubiquitin promoter, but to a ubiquitin regulatory system that includes the promoter as described above and the additional elements that participate in the modulating gene expression.
In the Monsanto patents, the ubiquitin regulatory system is modified by excising the heat shock elements. While In the Prodigene patent, the ubiquitin regulatory system is modified by making the two overlapping heat shock elements adjacent.