A sixth DNA base has been identified by researchers, adding to the five that were known to occur in the natural world. An international team of investigators recognized the new building block of genetic code and described its function in algae, insects and worms.
Genetic material manages and directs proteins that carry out many of the functions in animal bodies and plants.
A chemical process known as methylation can modify DNA, radically altering the expression of genes in living organisms. The four bases in animal DNA are adenine, thymine, cytosine and guanine, while RNA contains uracil in the place of thymine. Methylated cytosine was traditionally viewed as the main DNA modification found in eukaryotes — cells with a true neucleus and organelles wrapped in a membrane.
An adenine DNA methylation, N6-methyladenine (6mA), has now been identified in algae, flies and worms that assist in regulating cellular function.
"Genes that have methylated cytosine have been associated with reduced gene expression. What's different about adenine methylation is that it is associated with more strongly expressed genes. It's a missing piece in the puzzle of regulation at the DNA modification level, and that's an exciting thing," said Laurens Mets, associate professor in molecular genetics and cell biology at the University of Chicago.
Epigenetics, the study of chemical reactions that guide genetic expression in living beings, reveals traits can sometimes be passed from parent to offspring without modifying genetic instructions.
"The human genome is not static. It contains dynamic DNA modifications that carry key inheritable epigenetic information passed among generations of cells," said Chuan He of the University of Chicago.
The position of the methylated bases in the genome of the three organisms was precisely determined, aiding in understanding how the unusual genetic base affects the genome of the species. The feature is related to a protein complex known as a nucleosome, which can normally be found at various places along the genetic code. In highly-expressed genes, nucleosomes space out into precise locations, but how they did this remained a mystery. The newly recognized DNA modification seems to direct this spacing, a result researchers did not expect to find during the course of their study.
Future research will examine methylated adenine in order to determine the evolutionary history of the genetic modification. A wide range of life-forms, including mammals, will be examined to determine where else 6mA may be found in the animal kingdom.
A trio of papers on the new advances in understanding the genetic code were published in the journal Cell.
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