Regulatory RNAs

This chapter highlights regulatory RNAs. RNA molecules can act as regulators by base-pairing with target RNAs or even DNA, or by binding metabolites or proteins, to block or facilitate the binding of other RNAs or proteins and bring molecules into proximity. Most base-pairing RNAs in bacteria are expressed in response to specific environmental conditions. The chapter then looks at microRNAs (miRNAs), small interfering RNAs (siRNAs), and Piwi-interacting RNAs (piRNAs). miRNAs are encoded by distinct genes and modulate translation and mRNA destabilization. siRNAs are generated through excision along the length of a double-stranded RNA of either external origin or endogenous origin and direct RNA interference and transcriptional silencing. Meanwhile, piRNAs are derived from repetitive regions of the genome, are associated with Piwi family Argonaute proteins, and repress the expression of diverse repeat sequences in the nucleus. The chapter also considers the viral defense role of CRISPR systems.