ABSTRACT
The increasing sophistication of biochemical techniques developed between the 1960s and 1980s identified other relatively abundant RNA species beyond the canonical trio of tRNA, mRNA and rRNA. These included spliceosomal RNAs (snRNAs) that guide splicing and other aspects of gene expression; small nucleolar RNAs (snoRNAs) that guide modifications of rRNAs, tRNAs and snRNAs, over 700 of which are encoded in the human genome and are precursors of other types of small RNAs; 7SL RNAs, essential components of the ‘signal recognition particle’ that target proteins to the endoplasmic reticulum for membrane insertion or secretion; 7SK RNAs, which act as negative regulators of transcription; enigmatic Y RNAs involved in DNA replication and stress responses; ‘vault’ RNAs involved in recycling of cellular components in lysosomes and the plasticity of neuronal synapses; ‘virus-associated’ RNAs that modulate the innate immune response; and rodent brain-specific transposon-derived RNAs that modulate behavior. In the 1980s RNAs were discovered to have self-splicing and cleavage activities and to catalyze both translation and splicing, leading to the conclusion that RNA was the primordial molecule of life, subsequently outsourcing enzymatic functions to the more chemically versatile proteins and its information functions to the more stable and easily replicable DNA. These early observations and examples of the structural and functional versatility of RNA were, however, largely interpreted as relics rather than a new dimension, and failed to disturb the status quo.
