Toward an understanding of the structural basis of translation

Abstract

The recently solved X-ray crystal structures of the ribosome have provided opportunities for studying the molecular basis of translation with a variety of methods including cryo-electron microscopy - where maps give the first glimpses of ribosomal evolution - and fluorescence spectroscopy techniques.

Figure 1

The basic function of the ribosome during the elongation phase of protein synthesis. Amino acids and their corresponding tRNAs and codons are numbered from the amino terminus of the polypeptide. The amino acid is attached to the CCA end of the tRNA and is then transferred to the previous amino acid in the chain. See text for more details. Adapted from [43].

Figure 2

The two ribosomal subunits, as visualized by cryo-EM, with tRNAs attached in the A, P and E sites. The L7/L12 stalk, normally invisible because of its flexibility, is indicated by the dashed contour lines.

Figure 3

Expansion segments in the secondary structure of yeast ribosomal RNA. (a) 18S rRNA; (b) 5.8/25S rRNA [44]. Expansion segments (ES) are labeled using Gerbi's nomenclature [45]. Small numbers refer to the helix numbering convention; Roman numerals refer to the RNA domains. Reproduced with permission from [14].

Figure 4

Structures of ribosomes from different species. The small subunit is on the left. (a) X-ray structure of the T. thermophilus 70S ribosome [12]. (b) Cryo-EM map of the E. coli 70S ribosome [46]. (c) Cryo-EM map of the yeast 80S ribosome [14]. Expansion regions are darker. The dashed line indicates a flat surface that suggests eukaryotic specialization of 60S subunit for association with a planar membrane. (d) Cryo-EM map of the mammalian mitochondrial ribosome [37]. Reproduced with permission from (a) [12], (b) [46], (c) [14] and (d) [37].