System-evolutionary view of RNA presence in living cells
Our guiding question for this article was: How did RNA adjust its life when the RNA world era came to an end? RNA has its practical execution side in the whole-cell systems setup serving critical functions in metabolism, compartmentalization, and in the RNA-DNA-Protein network, coupling information handling and different events of macromolecule production into a self-sustaining loop. Aligning with current views of cooperation we find that RNA life is distributed across a population of information-bearing entities persisting by compatibility, with DNA serving as a long-term memory and proteins offering the catalytic reach. We suggest that the reproduction-survival axis, relevant to higher organisms, is also manifested by RNA in many forms, including RNA-primers, mRNAs, tRNAs, and rRNAs. Each of these have contrasting, highly adapted molecular phenotypes. Ultimately, we wish to emphasize the evolutionary narrative where RNA did not lose in exchange for DNA genes or otherwise. Ultimately, RNA just changed strategy and in its various forms has an active and critically important presence in all cells at all times.