Scientists at the University of Illinois and the University of California (USA) have identified a mechanism that could play a crucial role in the emergence of complex multicellular life in bacteria. According to researchers, non-coding genetic elements originally existing microorganisms, contributed to the increase in the size of the genome and the specific organization of DNA in eukaryotes. About it reported in a press release on EurekAlert!.
It is known that almost half of all human DNA consists of retrotransposons, the genetic elements (sometimes called genetic parasites) are able to move and reproduce within the genome. In bacteria they are practically absent. The attempt of scientists to transfer human retrotransposon in the cell of the bacteria led to the death of the latter. This was due to the fact that mobile genetic elements were integrated into genes that are vital for bacteria.
Eukaryotes have several mechanisms to repair DNA damaged by the retrotransposon. One such mechanism is homologous to a connection end joining (NHEJ), in which the ends of the cut DNA are stitched together directly. The possible loss of whole DNA fragments. However, the transfer of such mechanism in the bacterial cells not only helped to restore the damaged genes, but also accelerated the destruction of the genome. This indicates that in eukaryotes there are specific mechanisms of regulation of the genome.
One such mechanism is spliceosome — structure consisting of RNA molecules and proteins, which remove non-coding sections (its introns are) from precursors of Mature mRNA. Introns characteristic of eukaryotic genes and the human genome there are more than 300 thousand. It is believed that the evolutionary precursor of spliceosome introns were the 2nd group of mobile genetic elements present in bacteria and is able to catalyze its own synthesis. Introns in its properties are very similar to the bacterial analogue of retrotransposons.
According to scientists, the introns of the 2nd group somehow ended up in the cells of early eukaryotes, and their interaction with the NHEJ led to the emergence of spliceosome. In some cases, spliceosome capable of alternative splicing, that is, of messenger RNA introns are cut some are not or, conversely, cut the exons (coding portions of genes). Thus, genes are able to encode multiple protein products that contributed to the complexity of living organisms.
In addition, biologists believe that the interaction of retrotransposons with NHEJ also contributed to the emergence of chromosomes, the three-dimensional structures, in which “wrapped” the genetic material of cells that affects the activity of many genes.
Video, photo All from Russia.