Tuesday, January 16, 2007
European team unexpectedly finds clues to origin of life
Scientists studying RNA interference* (RNAi) (Overview | Animation), a recently discovered phenomenon with wide-ranging implications for biology and health, have stumbled upon what they believe may be an important clue to the origins of life itself. Researchers from Oxford and Helsinki University were studying the mechanism behind RNAi when they noticed that the core of the enzyme responsible for the process was strikingly similar to enzymes responsible for gene expression. Their find sheds light on the function of RNA and helps answers some puzzling questions biologists have faced for years.
Biology, and life in general for that matter, exists in a DNA-centred world where DNA holds our genetic information and with it controls how living organisms function. DNA communicates its critical information through the formation of proteins, which in turn carry out the tasks of everyday life. This situation, however, gives rise to a chicken-and-the-egg situation that has long perplexed scientists: How can DNA orchestrate the formation of proteins while it is itself made of proteins.
A recent article (see below) detailing the findings by Paula S. Salgado, Jonathan M. Grimes and colleagues published in Public Library of Science Biology (PLoS) explains how the similar enzyme structure led them to suspect that both derive from a single ancestor. Their discovery lends credibility to the theory that life actually began with the genome contained in self-replicating RNA which later evolved into DNA.
Researchers find this scenario conceivable for several reasons, and partly due to the fact that RNA has two major advantages over DNA. RNA, though chemically similar to DNA, is comprised of less complex materials making it more likely to have occured spontaneously. Additionally, it is easier to believe that RNA evolved into DNA, and not vice versa for example, because DNA is chemically more stable.
The new approach to RNA taken by the research team has the potential to help scientists in other areas of genetic research as well. DNA dictates the creation of proteins in a two-step process. Firstly, DNA's genetic information is converted into RNA, which in turn reacts with enzymes to produce proteins. However, approximately 30 percent of the genome converted into RNA never results in protein synthesis, violating one of Nature’s most basic laws. A process which consumes energy but does not lead to something advantageous should normally be weeded out by natural selection.
Since this is not the case with "junk" RNA, scientists have begun to suspect that it does indeed serve some beneficial end for the organism. For example, RNAi, the original focus of Drs Salgado and Grimes’ team, is located in these previously ignored sections.
RNAi, as its name implies, influences gene selection and has far-reaching implications for health and well-being. The 2006 Nobel Prize in Physiology or Medicine was awarded to the scientists responsible for its discovery**. The recent research concerning the multifaceted properties of RNA suggests that it has a bigger role to play in gene regulation than previously thought, in addition to the insights it may hold into the origins of life. [Source: European Commission Research Report]
Based on the open access/free PLoS Biology research article:
The Structure of an RNAi Polymerase Links RNA Silencing and Transcription
Citation: Salgado PS, Koivunen MRL, Makeyev EV, Bamford DH, Stuart DI, et al. (2006) The Structure of an RNAi Polymerase Links RNA Silencing and Transcription. PLoS Biol 4(12): e434 doi:10.1371/journal.pbio.0040434
RNA silencing refers to a group of RNA-induced gene-silencing mechanisms that developed early in the eukaryotic lineage, probably for defence against pathogens and regulation of gene expression. In plants, protozoa, fungi, and nematodes, but apparently not insects and vertebrates, it involves a cell-encoded RNA-dependent RNA polymerase (cRdRP) that produces double-stranded RNA triggers from aberrant single-stranded RNA. We report the 2.3-A resolution crystal structure of QDE-1, a cRdRP from Neurospora crassa, and find that it forms a relatively compact dimeric molecule, each subunit of which comprises several domains with, at its core, a catalytic apparatus and protein fold strikingly similar to the catalytic core of the DNA-dependent RNA polymerases responsible for transcription. This evolutionary link between the two enzyme types suggests that aspects of RNA silencing in some organisms may recapitulate transcription/replication pathways functioning in the ancient RNA-based world.
*See the Tuesday, December 05, 2006 post "Evolution: RNA Silencing Sheds Light on the RNA World"
**See the Tuesday, October 03, 2006 post "RNA Interference: Open Access to Nobel Prize Winners Original Paper"
A related post from Monday, January 15, 2007 "Closing a loophole in the RNA World Hypothesis"
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