New nucleotide

Back in my day, we just had adenine, cytosine, thymine, guanine, and uracil. Scientists have recently discovered a new base pair, 5-methylcytosine that replaces cytosine's place.

Its placement helps to regulate gene expression and expands the possibilities of manipulation by scientists. It works with methylation to determine which genes are expressed or muted.

What this nucleotide does is not yet clear. Initial tests suggested that it may play a role in demethylating DNA, but Kriaucionis and Heintz believe it may have a positive role in regulating gene expression as well. The reason that this nucleotide had not been seen before, the researchers say, is because of the methodologies used in most epigenetic experiments. Typically, scientists use a procedure called bisulfite sequencing to identify the sites of DNA methylation. But this test cannot distinguish between 5-hydroxymethylcytosine and 5-methylcytosine, a shortcoming that has kept the newly discovered nucleotide hidden for years, the researchers say. Its discovery may force investigators to revisit earlier work. The Human Epigenome Project, for example, is in the process of mapping all of the sites of methylation using bisulfite sequencing. "If it turns out in the future that (5-hydroxymethylcytosine and 5-methylcytosine) have different stable biological meanings, which we believe very likely, then epigenome mapping experiments will have to be repeated with the help of new tools that would distinguish the two," says Kriaucionis.

Via EurekAlert.