Working out whether proteins or nucleic acids came first was a chicken and egg puzzle that vexed scientists for decades. Genes made of nucleic acids (DNA or RNA) contain the instructions for making proteins, but enzymes made of proteins are needed to replicate genes. The discovery of the catalytic activity of RNA seemed to solve the paradox. Now, William Scott of the University of California, Santa Cruz, and colleagues have obtained an image of the ribosome with almost atomic resolution, which they explain sheds new light on the workings of this enigmatic nucleic enzyme mimic. "The structure illustrates unambiguously how functional groups of the RNA mediate acid-base chemical catalysis, permitting us to suggest that acid-base chemistry is so fundamental to enzyme catalysis that it predates the origin of protein enzymes," Scott says. In other words, he and his colleagues have perhaps cracked the chicken and egg of the RNA world once and for all.
A genetic chicken and egg