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Analysis of 'junk' DNA throws up surprises

19 June 2007
Appeared in BioNews 412

The universally accepted maxim that genes are transcribed into RNA and subsequently translated into proteins, a concept that has underwritten huge swathes of research in the last 40 years, has been significantly muddied. A groundbreaking Nature paper has shown the road from genome to protein is much more complex than previously suspected.

Entitled 'Encode' (Encyclopaedia of DNA Elements), a collaborative effort featuring 80 different organisations, the project aimed to hold a powerful magnifying glass to the intricate machinations of a single segment of DNA, representing one per cent of the human genome.

Head of Encode's analysis efforts, Ewan Birney, of the European Molecular Biology Laboratory's European Bioinformatics Institute, said: 'The Human Genome Project gave us the letters of the genome, but not a great deal of understanding. The Encode project tries to understand the genome'.

The genome is thought to contain around 22,000 genes. The coding sequence that represents these genes adds up to a mere three per cent of the entire genome. Until now, the remaining 97 per cent has been largely written of as 'junk'. If Encode's research is confirmed, it will prove this moniker is not just a mild misnomer, but highly inaccurate.

The new research suggests that 'junk' DNA, whose function has traditionally been thought of as merely architectural, allowing the sparse distribution of genes along the DNA filament, is, in fact, quite frequently transcribed into RNA. Segments adjacent to genes and, most surprisingly, regions located large distances from any known coding region are all transcribed into RNA; however, this RNA is not transcribed into protein.

Debate is raging as to whether the transcribed RNA has a function, perhaps in the transportation of molecules around the cell or to fine-tune and modulate the activity of genes, or whether it is just an evolutionary quirk, where the segments are transcribed due to a benign mutation and are maintained as they neither harm nor aid the cell. Tom Gingeras of genomics firm Affymetrix in Santa Clara, California, and a co-leader of ENCODE, said 'We don't think they're produced by accident'.

Genome project turns up evolutionary surprises
Nature |  14 June 2007
Human genome further unravelled
BBC News Online |  14 June 2007
'Junk' DNA makes compulsive reading
New Scientist |  13 June 2007
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