Chapter 19 - Noncoding RNA

Abstract

Noncoding RNA refers to all those RNA molecules that play biological roles as RNA, rather than being translated into protein like messenger RNA. Transfer RNA and ribosomal RNA take part in protein synthesis. Occasional RNA molecules act catalytically, as RNA enzymes (ribozymes) or take part in protein export. Two other major roles for noncoding RNA are in genome defense and in genetic regulation. Small noncoding RNA molecules take part in RNA interference in eukaryotes and in CRISPR in prokaryotes. Both systems protect against viruses and other hostile genetic elements. A wide variety of noncoding RNA molecules, both long and short, are involved in regulating gene expression. There are major differences between prokaryotes and eukaryotes. Prokaryotes use relatively few regulatory RNAs and these are usually short. Eukaryotes have a much greater variety of regulatory RNA molecules, including long noncoding nuclear RNA (lncRNA). In addition, in eukaryotes, several classes of small RNA take part in the processing of mRNA, tRNA and rRNA inside the nucleus.