Thursday, May 21, 2009

The Evolutionary Utility of Junk DNA

A Functional Role for Transposases in a Large Eukaryotic Genome. 2009. Nawacki, M., et al. Science 324: 935-938.

Captain Victory © Jack Kirby
Scientists have long been perplexed by the extensive strands of genetic material that dominate the genome - junk DNA - but seem to lack specific functions. Why would nature force the genome to carry so much excess baggage?
Researchers studying the genome of a pond organism have found that DNA sequences from regions of what had been viewed as the "dispensable genome" are actually performing functions that are central for the organism. They have concluded that the 'junk' genes spur an almost acrobatic rearrangement of the entire genome that is necessary for the organism to grow.

Genes called transposons in the single-celled pond-dwelling organism Oxytricha produce cell proteins known as transposases. During development, the transposons appear to first influence hundreds of thousands of DNA pieces to regroup. Then, when no longer needed, the organism cleverly erases the transposases from its genetic material, paring its genome to a slim 5 percent of its original load.

The term "junk DNA" was originally coined to refer to a region of DNA that contained no genetic information. Scientists are beginning to find, however, that much of this so-called junk plays important roles in the regulation of gene activity. No one yet knows how extensive that role may be. link