It's not Junk

Jul 2017
Junk DNA - Nessa Carey - Icon Books, 2015
* * *
This book has a number of annoying features, of which the most irritating is its downright fallacious title. This is something of a personal matter, because it relates to what is probably my most cited academic paper, a report by the DNA committee of the Human Genome Mapping 10.5 workshop held in Oxford in 1990. Needless to say, this had nothing to do with my research. As a post-graduate student, I was recruited as a runner for the committee, passing messages on good old-fashioned paper to the other committees (there was one for each chromosome). I got on so well with the chairman that he insisted on listing me as an author of the report. Anyway, the committee's job was to assess some DNA sequences that were not part of genes but which were nonetheless of scientific interest. So I like to think that in a small way, I contributed to the most surprising discovery of the Human Genome Project, which was that just 2% of the 3 billion DNA bases in the human genome are in genes (defining a gene as a sequence that codes for a protein). The remaining 98% appear to have no obvious purpose, though some sequences are highly conserved. So what are they doing there?

When I was an active academic, there were a number of hypotheses. One was that it is simply junk, an artefact of evolution that nature hasn't got around to clearing up. Another was that it is involved in the structural organisation of genes. Each human cell contains around 1800 mm of DNA packed into a nucleus just 0.006 mm in diameter, so ensuring that genes are physically accessible to the transcription enzymes that start the process of protein creation is clearly an important consideration. A third involved the interesting new area of epigenetics, a form of gene control based on chemical modification of the DNA and its scaffolding proteins. Now, some 25 years later, a great deal more research has been done and a great deal more is known. So which of these hypotheses is true? Well, this is nature, so the answer is - all of them, at least to some extent. But the one that is least true is that it is junk.
( Read more... )