Chapter overview: Many functional RNAs are never translated. This chapter organizes housekeeping and regulatory s, explains RNA interference and splicing, and examines how s guide, scaffold, decoy, and sponge other regulatory molecules.
Learning Objectives
Define by function rather than by absence of importance.
Compare tRNA, rRNA, snoRNA, snRNA, miRNA, siRNA, and piRNA.
Explain RISC-mediated silencing.
Describe spliceosome assembly and function.
Compare guide, scaffold, decoy, and sponge actions of lncRNAs.
The functional non-coding transcriptome
Introduction: Beyond the Central Dogma
For decades, the framework of molecular biology has been defined by the Central Dogma: DNA makes RNA, and RNA makes protein. This linear flow of information, from the genetic blueprint encoded in DNA to the functional machinery of proteins, remains fundamental to our understanding of biology. But the deeper we explore the genome, the more we realize that this model is only part of the story.
Less than 3% of the RNA transcribed from our genome actually gets translated into proteins. The rest, a massive and diverse collection of RNA molecules, does not code for proteins but instead plays critical roles in regulating gene expression, modifying , guiding cellular localization, and managing protein fate. These s (ncRNAs) are not the passive byproducts of ; they are active participants in cellular control systems that rival, and often direct, the influence of protein-coding genes.
In this chapter, we'll explore both short and s, with particular emphasis on their molecular mechanisms, cellular functions, and roles in epigenetic regulation. We'll also examine how localization signals, post-translational modifications like phosphorylation, and degradation signals like ubiquitination fit into the broader landscape of gene regulation.
Section 1: The Short Non-Coding RNAs
Short s are typically under 200 nucleotides in length, and while they may be small, their influence is vast. The most well-known members of this group include: