The ENCODE consortiums major findings include the discovery that the majority of DNA in the human genome is transcribed into functional molecules, called RNA, and that these transcripts extensively overlap one another. This broad pattern of transcription challenges the long-standing view that the human genome consists of a relatively small set of discrete genes, along with a vast amount of so-called junk DNA that is not biologically active.
The new data indicate the genome contains very little unused sequences and, in fact, is a complex, interwoven network. In this network, genes are just one of many types of DNA sequences that have a functional impact. Our perspective of transcription and genes may have to evolve, the researchers state in their Nature paper, noting the network model of the genome poses some interesting mechanistic questions that have yet to be answered.
Other surprises in the ENCODE data have major implications for our understanding of the evolution of genomes, particularly mammalian genomes. Until recently, researchers had thought that most of the DNA sequences important for biological function would be in areas of the genome most subject to evolutionary constraint that is, most likely to be conserved as species evolve. However, the ENCODE effort found about half of functional elements in the human genome do not appear to have been obviously constrained during evolution, at least when examined by current methods used by computational biologists.
According to ENCODE researchers, this lack of evolutionary constraint may indicate
Contact: Geoff Spencer
NIH/National Human Genome Research Institute