"In between the genes and the sequences known to regulate their activity are long, tedious stretches that appear to do nothing. The term for them is "junk" DNA, reflecting the presumption that they are merely driftwood from our evolutionary past and have no biological function.
But the work by the ENCODE (ENCyclopaedia of DNA Elements) consortium implies that this nuggets-and-dross concept of DNA should be, well, junked.
The genome turns out to a highly complex, interwoven machine with very few inactive stretches, the researchers report.
Genes, it transpires, are just one of many types of DNA sequences that have a functional role.
And "junk" DNA turns out to have an essential role in regulating the protein-making business.
Previously written off as silent, it emerges as a singer with its own discreet voice, part of a vast, interacting molecular choir.
"The majority of the genome is copied, or transcribed, into RNA, which is the active molecule in our cells, relaying information from the archival DNA to the cellular machinery," said Tim Hubbard of the Wellcome Trust Sanger Institute, a British research group that was part of the team.
"This is a remarkable finding, since most prior research suggested only a fraction of the genome was transcribed.""
Hmmm. What about the endogenous retroviruses.
I was under the impression that geneticists have been having doubts about junk DNA really being junk for some time now.
Regardless, it's nice to see that validated, although it'll make genetic engineering more complicated.
Actually, in the gene-tech community it has been acknowleged for some years now that non-coding ('junk' to the layman) DNA does indeed serve a purpose in higher order organisms. Parts of this material really is junk insofar as we can tell, and all of it is in many plants and simpler organisms. However, even though it may not code for a protein, it often still serves a function - regions of it act as 'error magnets', as certain replication errors can travel along a DNA strand and due to their exact electronic configurations certain sequences of bases can 'trap' such errors and prevent them affecting critical gene coding regions. Furthermore, short portions of these segments code for short fragments of RNA whose sequence is a match for a short part of an mRNA strand and can bind to it, thus disabling it. These fragments, called iRNA (I believe, I'm out of touch now) 'interfere' with the process of reading RNA by the ribosomes by literally blocking part of the RNA. By activating the production of these pieces of RNA it becomes possible to regulate the expression of the mRNA, giving fine-tune control over gene expression. This tends to be observed only in more complex organisms, and the effect is (I would guess) a happy coincidence arising from the accumulation of a bulk of useless non-coding DNA, which has since been tuned by evolution as once it emerged it would modify the organism's structure just like any gene.
A more interesting thing to note is that what was once held as a large quantity of irretrievably corrupted genetic data on the Y chromasome was in fact a mirror of the coding genes which are Y-exclusive (the Y chromasome has some genes in common with X, as well as some unique ones. Sorry ladies, it ain't just a cripple X - guys actually have greater total genetic complexity, at the expense of some redundancy). Recent research has shown that the Y chromasome can fold back on itself in a curious variation on standard genetic auditing processes to self-correct on the grounds that the 'non-coding' region, being accessed less often, is more stable. Which bit is the non coding bit is readable due to the differing orientation of the deoxyribose 'spinal' units of the helix.
Sorry for the Xbox post.
Aaaaand I misspelled chromosome throughout. Whoop de fucking doo, aren't I clever. Oops.
Micro RNAs (miRNAs) have been characterised in the last 5 years. As mentioned by >>5, they regulate gene expression at transcriptional level, the difference between miRNAs and RNAi is that the origin of the second is exogenous while the first is regulated by the cell.
The RNAi mechanism is thought to have evolved (some think it was independent among the organisms that have it) as protection against viruses.
miRNAs on the other hand can act in a regulon-like manner as they are regulated by the cell through genes that code solely for miRNAs (others are coded within introns) and have affinity to a group of genes which means that many genes can be regulated at once. This whole novel area of research undermines our definition of a gene.
I was about to describe the function of the risc complex but I suppose and image (in this case video) is worth more than I could explain:
http://www.nature.com/focus/rnai/animations/index.html
Enjoy!