packing genes
New research has cast doubt on the idea that active genes are always in ‘open’ DNA conformations and inactive genes are in tightly packed regions of chromosomes.
The human genome’s DNA is packaged with proteins into ‘chromatin’, which can adopt different higher-order structures – such as the highly condensed form seen in chromosomes during cell division.
Active genes are thought to lie in regions of ‘open’ chromatin, so control proteins can gain access to them, while inactive genes have been presumed to be in tightly packed ‘compact’ chromatin. However, new research from the Wellcome Trust Sanger Institute and the MRC Human Genetics Unit in Edinburgh shows that this is not necessarily the case.
The team analysed chromatin across the entire genome, and found that regions rich in genes did tend to be in open chromatin structures, whereas regions poor in genes tended to be in compact chromatin. But it was not black-and-white: open chromatin could contain inactive genes and compact chromatin could contain active genes.
An understanding how these open and closed chromatin structures are formed, and how genes in closed chromatin can be read, will be important for understanding how genes are turned on and off. Now we know that the number of genes in the human genome is surprisingly small – just 23 000 or so – attention is focused on how the activity of these genes is controlled.
Future studies will investigate whether open and closed chromatin structures change in disease such as cancer.