Research in the September issue of Nature Genetics may shed new light on one of the key hurdles associated with the development of life on Earth -- how to evolve genetic complexity.
One of the problems with the theory that living cells evolved from replicating molecules comes from the inherent imperfection of the copying process. Larger and more complicated molecules might be capable of preventing or correcting their mistakes (mutations), but then the target to be copied is larger too, increasing the chance of mutations. This dilemma, called an "error threshold" was thought to present a lethal block to the evolution of complex molecules.
Eors Szathmáry and colleagues have calculated that many mutations may not after all be lethal to real replicators. They examined the effects of real mutations (copying mistakes) on the predicted structure of real RNA enzymes, called ribozymes, and found that many mutations are likely to have no effect, or even to cancel out the damage caused by other mutations. This reprieve from "mutational meltdown" is enough to allow a genome size of seven thousand bases or RNA "letters", which is big enough to allow the survival of a minimal genome in the RNA world. The idea of an error threshold is still of great interest as a way to battle viruses today by using drugs to drive the virus's copying process beyond the level of mistakes it can tolerate.
Eors Szathmary (Collegium Budapest, Institute for Advanced Study, Hungary)
Additional contact for comment on paper:
Edward C. Holmes (Penn State University, University Park, PA, USA)
For abstract, click here.
(C) Nature Genetics press release.
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