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Tuesday, 03 September 2013 17:23

New method for turning genes on and off could enable more complex synthetic biology circuits

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CRISPR-mice-virus-detection-teratoma-teratoma-service-ipsc-transgenic-mouseMIT researchers have shown that genes on or off in yeast and human cells by controlling, when DNA into RNA - bypokrok that will allow scientists to better understand the function of these genes copy.
This technique can also be easier to control the environment of the cell produkujídrogy or disease realize engineer, says Timothy Lu, assistant professor of electrical engineering and computer science and bio - engineering and lead author of a paper describing the new approach in the journal ACS Synthetic Biology.
"I think it will be much easier to build synthetic circuits" says Lu, a member of the Synthetic Biology Center at MIT. "It should increase the extent and speed with which we can build a number of synthetic circuits in yeast and mammalian cells."
The new method is based on a system of viral proteins have been used recently for the treatment of genomes of bacteria and human cells. Initial system called CRISPR consists of two parts: a protein which binds to DNA and washers and a short strand of RNA, leaders of the protein into the correct position in the genome.
"CRISPR system is so powerful that it can be used for a variety of DNA - binding regions of a simple conversion of this handbook RNA targeted basis" says Lu. "By simply reprogramming the RNA sequence of this protein can be any place you want to call the genome or synthetic circuit."
The main author of the article is Farzadfard Fahim, an MIT graduate student of biology. Samuel Perl, student of Electrical Engineering and Computer Science, is takéautorem.

Targeting transcription

In previous studies CRISPR was used to cut pieces of the gene is switched off or replace it with another gene. Lu and his colleagues decided to use the CRISPR system for a different purpose : control of gene transcription is the process by which DNA sequence into RNA (mRNA ), which goes beyond genes copied instructions.
Transcription is strictly regulated by proteins called transcription factors. These proteins bind to specific DNA sequences in the promoter region of the gene, and either modify or block the enzymes needed for the copy of the gene into mRNA.
Which acts as a transcription factor for this study, the researchers adjust CRISPR system. Firstly, the modified CRISPR normal protein known as time9 so that it no longer cut the DNA bound thereto. They are also added to the protein, the segment that is activated or suppressed by modulating gene expression machinery of cellular transcription.
Time9 to get to the right place, the researchers also corresponds delivered to the target cells, the genes for RNA guides who chtějísekvence DNA activates the promoter of the gene.
Researchers have shown that when the guide RNA and protein time9 connection in the target cell, the target gene přesněpravý atranskripce. To their surprise, the same complex time9 also used to block transcription to be found in other parts of the gene.
"It's nice that allows you to make a positive and negative regulation of the same protein, but with different RNA targeted to various managerial positions in the promoter" says Lu.

"A lot of elasticity"

The new system should be much simpler than other newly developed two systems for the transcription of DNA - binding proteins such as zinc finger transcriptional activator and effector Nucleases ( Talens ) is known, says Lu. Although effective, the construction and assembly of proteins is time- consuming and expensive.
"There is a lot of flexibility with CRISPR, and it really comes from the fact that you do not spend more time in protein engineering. You can only change the sequence of the nucleic acid RNA, " says Lu.
"The fact that this can be used for effective regulation of transcription in both yeast and mammalian cells, it is very encouraging," says Kobi Benenson, Professor of Biosystems Science and Engineering at ETH Zurich, which is not part of the research team." This technology may be used in the very near future genetic engineering and synthetic biology applications for biopharmaceuticals - "Tissue engineering and gene therapy, among other things"
Researchers also transcriptional control designed so that it can be triggered by specific small molecules, which may be included in the cell, such as sugars. For this, the guide RNA genes constructed so that they are only produced Primal molecule is available. No small molecules, there are no guidelines aRNA gene is targeted at rest.
This type of control could be used to explore the role of naturally occurring genes on and off at specific times during development or progression useful, says Lu.
Lu is now working on the development of advanced synthetic circuits for applications such decisions are based on multiple inputs made ​​by the mobile environment. " We want to be able to scale- up the most complex circuits and show that anyone is ever built in yeast and mammalian cells" he says.

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