Since the discovery that RNA molecules can act as catalysts in chemical reactions, they have become prime candidates for being the kick start that life on Earth need billions of years ago. Although the conventional explanation is that proteins were cooked up in the primordial oceans and ultimately became parts of living organisms, there is no clear way to get from proteins appearing randomly to self-organising systems based on proteins.
Although proteins can make efficient catalysts, they have no clear way to reproduce. RNA is now a much more likely candidate as it can pass on genetic information and catalyse the reactions needed to do it. Although proteins are now responsible for most of the body’s catalysis, RNA ‘ribozymes’ are still in active and can be found at the heart of what are understood to be some of the most ancient cellular functions.
RNA plays a key role in the translation process used to make proteins from a template encoded in RNA. The chances are, according to the ‘RNA World’ theory, that RNA made more RNA templates before life became complex enough to depend on a mixture of RNA and proteins. But this leaves the question of how a sufficiently complex ribozyme came about that could catalyse production, at the very least, copies of itself.
But, what if a self-replicating ribozyme could be very simple? How simple could it be? Publishing in PNAS, a team from the University of Colorado at Boulder has found a very simple ribozyme. It has just five bases but is able to catalyse reactions with other segments of RNA. It’s not very quick, but it works and, unlike previous work on simple RNAs, does not depend on metal ions for the catalytic activity.
The work by Professor Michael Yarus hints that RNA may put together proteins quite readily. “Essential intermediates in protein biosynthesis arise surprisingly easily in the presence of very short RNAs,” they write.
“The ultimate importance of these observations may lie partly in the unknown number of other reactions that can be accelerated by comparably small RNAs. This is because for each such minuscule RNA reaction, there is a prima facie case that it would become accessible even after the most primitive ribonucleotide polymerisation.”
It’s possible that this simple catalyst is a one-off, Yarus and colleagues warn. “On the other hand, it will be extraordinarily important to look for other tiny RNA active centres, now knowin they can exist.”
It makes the RNA World hypothesis look more likely and may help in the development of very simple synthetic cells for bioproduction.
