An article published in the journal “Proceedings of the National Academy of Sciences” describes a study on the possible precursors of RNA. A team of Harvard University biologists led by Nobel Prize laureate Jack Szostak is trying to reconstruct the various steps that led to the birth of life with lab experiments and an interesting result came from the use of inosine (image of its molecular structure ©NEUROtiker) as a surrogate for guanine, one of the RNA and also DNA bases.
For decades, many scientists have been trying to replicate the phases of DNA formation starting from the ingredients existing on the primordial Earth. Many of those phases have been reconstructed but some are still confined to theory. In particular, many biologists are working on the steps that led to the formation of RNA, which may have preceded DNA but there are problems in understanding the formation of two of its bases, adenine and uracil, while progress in understanding the formation of the other two bases, cytosine and guanine, are much greater.
Jack Szostak is a biologist who carried out a number of studies on RNA and DNA throughout his career and received the Nobel Prize in Medicine in 2009 for the studies he carried out with his colleagues Elizabeth H. Blackburn and Carol Greider on role of telomeres in chromosome protection. In recent years he’s among the biologists who are studying the origin of life, a complex subject matter as the oldest fossil traces are of life forms with a level of complexity much higher than DNA molecules and even higher than RNA molecules.
Some of life building blocks have been found even in space since even in those conditions there may be enough energy for simpler compounds to combine, although it may take millions of years to reach certain levels of complexity. Traces of cyanoacetylene, a precursor of cytosine, were found in the Orion cloud and in other interstellar clouds but also in the solar system, in the Hale-Bopp comet’s coma and in the atmosphere of Titan, the great moon of Saturn where there are ongoing complex chemical reactions and for this reason is the object to attention by astrobiologists.
Jack Szostak’s team explained that they took a step forward in explaining the formation of RNA using inosine, which is formed by hypoxanthine with a ribose ring attached, as a surrogate of guanosine, formed by the RNA and DNA base guanine with a ribose ring attached. Inosine is present in cells and is important in protein synthesis so it could be a compound connected to life forms from the beginning.
Among several possible precursors of guanosine, inosine is the one that in lab tests was found to work, meaning that it’s the one that allowed the RNA variant based also on it to replicate quickly and with few errors. Seohyun Kim, Harvard graduate student and first author of this study, explained that the first life forms might have been born from a set of bases different from the one we find in RNA and even more in DNA proposing inosine among the original bases.
This research could be a step forward in proving that life on Earth was born with RNA but it doesn’t mean that’s the only possibility. Different paths may lead to RNA or other nucleic acids that are a little different from RNA and DNA. This study was reported in the field of astrophysics and of astrobiology as well for the interest in life building blocks that are found in space and the possibilities that Earth-like life forms of Earth might develop on other planets or on moons such as Titan but also on those with underground oceans such as Jupiter’s great moon Europa and Saturn’s moon Enceladus.