The RNAWorlds in Context

SUMMARY TherearetwoRNAworlds.ThefirstistheprimordialRNAworld,ahypotheticalerawhenRNA served as both information and function, both genotype and phenotype. The second RNA world is that of today’s biological systems, where RNA plays active roles in catalyzing biochemical reactions, in translating mRNA into proteins, in regulating gene expression, and in the constant battle between infectious agents trying to subvert host defense systems and host cells protecting themselves from infection. This second RNAworld is not at all hypothetical,andalthoughwedonothavealltheanswersabouthowitworks,wehavethetoolstocontinue our interrogation of thisworld and refine our understanding. The fun comeswhen we try touseoursecureknowledgeofthemodernRNAworldtoinferwhattheprimordialRNAworld might have looked like.