Following the completion of the Human Genome Sequencing Project, molecular genetic researchers discovered another type of genetic code in August, this time housed outside of DNA.
The recently discovered code is thought to control how genes are activated or inactivated rather than dictate gene location and function, which was what the Human Genome Project initially aimed to uncover.
According to David Allis lab, which housed the University's research efforts, the new code could influence the future of disease, aging and cloning by being able to turn on or off "unwanted" genes.
The gene regulation mechanism is a process called histone methylation. Histones are proteins that mediate the folding of DNA into a stable structure called chromatin.
At the fourth (K4) and ninth (K9) positions of the histone tail, the amino acid lysine exists.
In the process of histone methylation, a chemical methyl group is added to either the K4 or K9 lysine to determine whether a gene will be activated or inactivated.
The histone methylation serves as a "master switch," multiplying the quantity of information that could be stored in the genetic DNA code.
The fact that the histone methlyation code can be deciphered and transcribed into biological processes suggests DNA is not the only source of our genetic blueprint. According to Allis, a professor of biochemistry and molecular genetics, the code is a second level of control, much like an address book that dictates where genes should be expressed.
But is this a second genetic code?
Gary Felsenfeld, a researcher from the National Institute of Health says no. The term "genetic refers to a code that can be transmitted from parent to offspring," he said. "For example, DNA is a genetic material."
Histone modification by methylation only makes it easier for chromatin to open up and be transcribed. No one has yet demonstrated that histone methylation can be transmitted among generations, making it a "genetic" code.
Histone methylation has been conserved evolutionarily in everything from fish to humans. In fact, at the Cold Spring Harbor Laboratory in New York, researcher Shiv I.S. Grewal, showed that Schizosaccharomyces pombe, a fission yeast, demonstrates patterns of methylation associated with gene regulation that are the same as those in higher organisms.
Felsenfeld's research produced similar results in chicken genes.
Histone methylation is a phenomenon "very much the same in very different organisms," Felsenfeld said. "From chickens, we can read humans"
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