Part human, part virus – what do we really know about DNA?

For all our progress, the mechanisms of life remain stubbornly elusive.

Biology continues to surprise us at every turn. In the past half-century, human beings have explored the whole of our solar system but it turns out that the greatest mystery may exist inside the explorers.

Researchers at the J Craig Venter Institute in the US have found the “minimal genome” of a microbe – the genes that are essential to the organism’s functioning. In a painstaking process that involved taking one out, then another, the researchers have whittled away at the “luxury” genes, reducing the microbe to its bare bones.

In the course of creating their minimal genome, the team discovered that a third of the essential genes perform completely unknown functions. It’s a chilling moment, because those genes are in each of our cells, too.

The aim was and still is to understand life: to discover how amino-acid chemistry gives rise to biology. The Craig Venter researchers are proper explorers, no less pioneers than the scientists, engineers and astronomers who have explored our solar system and beyond. And as with outer space, it is the things we fail to discover which are most exciting. It’s no wonder that the mystery genes have been described as biology’s “dark matter”.

For all our progress, the mechanisms of life remain stubbornly elusive. More than 60 years ago, Stanley Miller and Harold Urey showed that you could create amino acids – the building blocks of genes – by jolting a mixture of ammonia, hydrogen, methane and water with an electrical discharge. We might not have known exactly how chemistry became biology but it did not seem too complicated.

Then came genes, with Francis Crick’s announcement in 1953 that he and James Watson had discovered “the secret of life”. A few decades later, we developed the technology to uncover the genetic recipe of every organism on the planet. Then, in 2010, Venter’s researchers created Synthia, the world’s first microbe with an artificially created genome. It looked as though we would soon be unpicking life’s greatest secrets.

But we are flummoxed once again. The smallest naturally occurring genome is Mycoplasma genitalium, which has 525 genes. Venter’s new organism, known as JCVI-syn3.0, has just 473 genes. Of these, 149 do something we do not understand – but that something is essential. When Venter’s team took any of them away, the organism died.

Just as exciting is the finding from Tufts University in Massachusetts that our DNA contains far more genes derived from viruses than we realised. Like the biological dark matter, this holds answers that biologists are keen to expose. Viral DNA makes up 8 per cent of our genome. We co-opted it when viruses infected our ancestors hundreds of thousands of years ago, inserting their DNA into each infected organism’s genome, and then passing them down the evolutionary generations.

Thanks to the Tufts researchers, we now know of an extra 19 pieces of viral DNA. There is probably more to find and it is worth finding, because our bodies have learned to put viral DNA to work.

Viral genes protect a developing foetus against toxins in the mother’s blood, for instance. Other viral genes control the ability of stem cells to develop into particular forms of tissue. There are hopes that viral DNA’s ability to control genetic switches will be useful in the fight against cancer and other diseases. If we are seeking out new frontiers, we need only look inward.