Non-canonical roles of tRNAs and tRNA mimics in bacterial cell biology

Abstract

Transfer RNAs (tRNAs) are the macromolecules that transfer activated amino acids from aminoacyl-tRNA synthetases to the ribosome, where they are used for the mRNA guided synthesis of proteins. Transfer RNAs are ancient molecules, perhaps even predating the existence of the translation machinery. Albeit old, these molecules are tremendously conserved, a characteristic that is well illustrated by the fact that some bacterial tRNAs are efficient and specific substrates of eukaryotic aminoacyl-tRNA synthetases and ribosomes. Considering their ancient origin and high structural conservation, it is not surprising that tRNAs have been hijacked during evolution for functions outside of translation. These roles beyond translation include synthetic, regulatory and information functions within the cell. Here we provide an overview of the non-canonical roles of tRNAs and their mimics in bacteria, and discuss some of the common themes that arise when comparing these different functions.

Figure 1. Structure of tRNA

Schematic representation of A) secondary and B) tertiary structure of tRNA. Tertiary structure is based on the backbone of yeast tRNA^Asp as in pdb model 1VTQ (Moras et al., 1980). The main parts of tRNA are highlighted in different colors, using darker colors for stems and lighter colors for loops. Used colors are red: acceptor stem, blue: deoxyuridine arm, gray: anticodon arm, cyan: variable arm, green: TΨC arm and orange: segments linking tRNA arms.

Figure 2. Biological roles of tRNA

Classification of the diverse roles that tRNAs play in cell biology. Functions of tRNAs were classified in 4 main groups, translation (blue), synthetic functions beyond translation (yellow), tRNA dependent regulation (red) and genomic interactions (green). Positioning of each group in the figure is not related to the parts of tRNA involved in specific functions.