DNA is not "junk"
A genome is not just a set of genes
Dmitry Tselikov, CompulentaThe human genome – the sum of inherited information – is, as it has just turned out, not only a set of protein-coding genes.
The Encyclopedia of DNA Elements (ENCODE) project, funded by the United States, began in the late 1990s with the intention of finding all the traditional genes in order to identify all the proteins necessary for life. Each gene was thought of as a discrete fragment of DNA, and the order of the DNA bases (the well–known "letters" - that is, the molecules that make up DNA) was considered the code of a specific protein. But, to their surprise, scientists found that such sites account for less than 3% of the genome. What is the meaning of billions of other reasons?
Now there is an answer to this question. It turned out that many of them play an important role in human biology: for example, they help determine when a gene is turned on or off. It is this circumstance that makes one cell a kidney cell, and the other a brain cell. "The genome is not just a set of genes," sums up co–author Mark Gerstein from Yale University (USA).
Insight into this essence will help researchers to better understand the relationship between genetics and diseases: an unprecedented accurate and comprehensive map has been compiled indicating the role of each specific foundation.
The ENCODE project, led by Evan Burney from the European Bioinformatics Institute (UK), involved 32 institutions and 442 specialists. They conducted a computer analysis, performed biochemical tests and examined the bases of 147 cell types (six of them with special care) in order to find out the role of each of the 3 billion bases. In general, it turns out that about 80% of the genome is biochemically active. Some sequences of nucleotides are designed to bind to proteins that affect the activity of genes. Others turn into strands of RNA, which themselves are able to perform a number of functions – gene regulation, for example. (RNA is generally regarded as an intermediary molecule that helps produce proteins, but ENCODE has shown that most of the RNA is the end product and is not used to create proteins.) And many parts of the genome simply provide a place for chemical modifications that disable selected parts of our chromosomes.
The ENCODE project has deciphered the structure of chromosomes with unprecedented detail. (ENCODE image.)
Thus, our understanding of genes is changing in a very fundamental way. It was found that about 76% of DNA is transcribed into RNA of one kind or another – much more than expected. This part of DNA includes slightly less than 21 thousand protein-coding genes (once it was assumed that we have more than 100 thousand of them), as well as the "genes" of 8.8 thousand small RNA molecules and 9.6 thousand long non-coding RNAs, each of which occupies at least 200 bases. Add to this 11,224 DNA regions that were classified as pseudogenes, that is, "dead" genes, and which, as it has just turned out, are actually active, but only in some types of cells or in individuals. Finally, it became known that genes can intersect and have several beginnings and ends.
In total, 4 million DNA sites have been found that act as switches of gene activity. These switches can be located both near and far from the gene they regulate. They act in various combinations in different types of cells in order to give them individuality. In addition, at least some of the RNA strands produced by the genome help control the amount of protein produced as a result of the activity of a particular gene. Thus, gene regulation turns out to be a much more complex process than previously thought.
The results of the study have been published in the journals Nature (six articles), Genome Research and Genome Biology (24 materials), as well as on the website of the journal Science (two articles).
Prepared based on the materials of ScienceNOW: Human Genome Is Much More Than Just Genes.
Portal "Eternal youth" http://vechnayamolodost.ru06.09.2012