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Team:Harvard/allergy/methods
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Revision as of 15:38, 4 August 2010
methods
As proteins provoke the majority of allergic reactions, we hope to diminish the allergenic properties of our plants by suppressing the expression of proteins that aren't necessary for the plant's survival but have been found to cause allergic responses in humans. This problem is complicated by the fact that proteins with allergenic properties may have several slightly different (but similar enough to remain allergens) homologues spread throughout the plant's genome. Subject to the constraint of the plant's survival, we would like to reduce or eliminate the expression of these homologues as well.New version:
Creating hypoallergenic plants is a complicated process. Many proteins that provoke allergic reactions are essential for the plant's survival, and plants frequently produce more than one version of the protein. Our ability to reduce and eliminate allergy-inducing proteins from a plant is constrained by what proteins the plants need for survival and our success in eliminating homologous versions of the offending protein.
When plants, or any organism, synthesize proteins, genomic DNA is transcribed into mRNA, which is then translated into a protein. In order to decrease or eliminate protein production , the genomic DNA coding for the mRNA can be removed, or transcription or translation can be stopped.
Removing regions of the genome that code for particular proteins is difficult. Not only are genomes difficult to alter without inadvertently damaging the organism, but genomic alterations have many limitations. For instance, the organism must have relatively few cells to effectively weed out unwanted DNA.
The preferred method of decreasing protein production in plants is through a process called RNAi, short for RNA interference. The general concept behind RNAi is to use special types of RNA to stop the translation of specific proteins.
RNAi
RNAi (RNA interference) is a process used to control expression of genes in living cells. It down-regulates gene expression by preventing the translation of specific proteins. In this process, the cell's machinery recognizes double stranded RNA sequences present in the cell. These sequences are then cut up into shorter fragments. mRNA transcripts that are complementary to these shorter sequences are then cleaved, thereby preveting trasncription of the proteins that would have come from these sequences. By introducing synthetic double stranded RNA sequences complementary to the sequences of the various allergens that we would like to target, we hope to knockdown the expression of these allergens and their homologues (versions of these allergens with a similar sequence that would still produce an allergic response).hpRNA
With RNAi, the problem of creating a hypoallergenic plant reduces to the problem of integrating short RNA strands into the RISC, each with complementarity to RNA which ribosomes would otherwise transcribe into allergenic proteins. One mechanism of flagging RNA for RISC-incorporation is to place the RISC-targeting sequence (~300bp), an intron-specific sequence (200-, and the reverse complement of the RISC-targeting sequence (~300bp) under a promoter (in nature these constructs could also be found in an intron). Upon transcription, this construct will form a hairpin: the targeting sequence and its reverse complement will anneal to each other while the intron-specific sequence will form the hairpin's loop. This structure is called a hpRNA, short for "hairpin RNA." The RISC will then process and incorporate part of one of the legs of the hairpin (targeting sequences) with which it will search for and destroy complementary RNA sequences.
