Mimicking how electrical engineers rearrange capacitors and resistors to create different electric circuits, geneticists can arrange gene promoters and suppressor genes to create gene circuits with different properties. In fact, such circuits have already been used to build a genetic clock and to synthesize cellular machinery that can follow basic logic commands such as AND, OR, and NOR.
Now the goal is to find a way not just to turn gene circuits on and off but to run and regulate them at intermediate settings.
Fluorescent Yeasts Demonstrate One Approach
By adding measured amounts of anhydrotetracycline (ATc), a derivative of the antibiotic tetracycline, to a population of genetically modified yeast cells, a research team at the University of Texas M.D. Anderson Cancer Center were able to precisely control the production and expression of a green fluorescing pigment in the yeast cells.
In the June, 2009 Discover magazine in an article entitled, "A Dial That Cranks Up Gene Action," Jeremy Labrecque reports that Cancer Center scientists found that doubling the concentration of ATc made the cells glow twice as brightly. Dramatic changes in cell function can result from even small changes in gene activity so this research may open up new approaches for studying gene function and cell response.
Another Approach is to Change Protein Structure
Genes carry the code that produces proteins to carry out almost all functions in a living organism. But some of these proteins also help control when and where genes do their jobs. A new study deals with how one such protein, named Ets-1, turns genes on or off.
Researchers from Huntsman Cancer Institute studied Ets-1, a protein known as a transcription factor that helps read genetic information. This factor serves as a cell’s "librarian", helping find the right genetic instructions.
A June 30, 2005 article entitled, "A 'Dimmer Sitch' for Genes," released by the News Center of the University of Utah state that according to team leader Barbara Graves, "What we found was that each time we added a phosphate to a particular unstructured region of Ets-1, there was an effect on the protein’s ability to bind to a gene. Binding was weakened, but it was a gradual weakening. "That isn’t typical," Graves says. "Instead of acting like an on-off switch, it behaved the way a dimmer switch does to regulate lighting in a gradual manner."
The scientists are baffled as to why Ets-1 worked differently before and after phosphorylation [the addition of phosphate], because as far as the scientists could tell, the overall shape of the molecule didn’t change. The findings have long-term implications not only for genetics but for the study of all proteins, because, according to Graves, any protein has the potential to be organized this way, with structured and unstructured regions that work together.
Genes Never Turn Off Completely
One of the central problems in regulating gene activity is that you can't get a completely 'off' configuration. Even when genetic switches are turned off, some of the protein that is meant to be repressed still gets made. One way to get around this is to snip out a gene entirely to stop production of a specific protein. However, this approach is irreversible and doesn’t really accord any degree of control or regulation.
To overcome these challenges, a biomedical team at Boston University came up with a design that combines two different technologies to repress and even tightly shut down gene expression. First, a repressor protein is positioned at a specific site on a DNA molecule. This protein acts as a barrier, preventing any messenger RNA (mRNA) from being made. Secondly, interfering RNA (RNAi) is used to seek out any mRNA gets past the protein repressor. The interfering RNA (RNAi) attaches to the functional mRNA, rendering it useless.
Most importantly, this switching method is both reversible and adjustable. By adding a chemical, Isopropyl-a-thiogalactopyranoside, the two-part repressor components are blocked and the gene turns on again. The gene's activity can be tuned up or down by adjusting the amount of this chemical.
Researchers demonstrated the effectiveness of their gene switching techniques by applying those techniques to the gene that produces diphtheria toxin in certain bacteria, then inserting the whole assemblage into live cells. One molecule of diphtheria toxin can kill a cell, but with the genetic switch turned off, the cells survived for weeks. When the researchers then allowed the diptheria gene to begin functioning, toxin production was initiated and the cells died.
Each of these lines of research holds the promise of better understanding the effects of genes operating at different intensities and offers hope for future applications of this research in therapies for genetic disorders.
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