The case of the missing allosteric ribozymes

The RNA World theory encompasses the hypothesis that sophisticated ribozymes and riboswitches were the primary drivers of metabolic processes in ancient organisms. Several types of catalytic RNAs and many classes of ligand-sensing RNA switches still exist in modern cells. Curiously, allosteric ribozymes formed by the merger of RNA enzyme and RNA switch components are largely absent in today's biological systems. This is true despite the striking abundances of various classes of both self-cleaving ribozymes and riboswitch aptamers. Here we present the known types of ligand-controlled ribozymes and riboswitches and discuss the possible reasons why fused ribozyme-aptamer constructs have been disfavored through evolution.

Automated summary

The RNA World theory suggests that sophisticated ribozymes and riboswitches played a key role in metabolic processes in ancient organisms, and various types of catalytic RNAs and ligand-sensing RNA switches still exist in modern cells. However, the fusion of RNA enzyme and RNA switch components to form allosteric ribozymes is rare in today's biological systems, despite the abundance of self-cleaving ribozymes and riboswitch aptamers.