Researchers at Emory University School of Medicine and the University of Chicago have developed a method for labeling and mapping a "sixth nucleotide," whose biological role scientists are only beginning to explore. The method is described onlin in Nature Biotechnology. The method allowed the researchers to see for the first time how 5-hydroxymethylcytosine (5-hmC) is distributed throughout the genome. Unlike 5-methylcytosine (5-mC), a chemical modification of DNA that is generally found on genes that are turned off, this extra layer of modification is enriched in active genes... 
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