After sequencing the human genome, the next logical step is to figure out how cells make use of this instruction manual. In Nature, researchers do just that, with the results of a huge project that identifies and analyses functional elements taken from part of the human genome.
Thirty-five groups provided over 200 data sets, comprising around 1% of the human genome, for the pilot of the Encyclopedia of DNA Elements (ENCODE) Project. Ewan Birney and an international consortium then described which parts of the selected DNA are transcribed into RNA, where specific proteins are bound to the DNA, how the sequence compares to that of other organisms, and what form the structure of chromatin (the complex of DNA and proteins that make up chromosomes) takes in the selectedÂ regions.
From this, the consortium derived a number of exciting new insights into both the nature and evolution of DNA sequences important for biological function. For example, most of the DNA studied appears to be transcribed into RNA, and these DNA transcripts overlap extensively. This is at odds with the view that the human genome contains a relatively small set of discrete genes alongside a mass of biologically inactive 'junk DNA'.
The team also found that around one-half of the genome's functional elements appears to be able to change sequence more freely than expected across mammalian evolution. This suggests the existence of a large pool of neutral elements that are biochemically active but provide no specific benefit to the organism, which may serve as a 'warehouse' for natural selection.
Zhiping Weng (Boston University, MA, USA)
John M. Greally (Albert Einstein College of Medicine, Bronx, NY, USA)
(C) Nature press release.
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