Structural information for explaining the molecular mechanism of protein biosynthesis

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Abstract
Protein biosynthesis is controlled by a number of proteins external to the ribosome. Of these, extensive structural investigations have been performed on elongation factor‐Tu and elongation factor‐G. This now gives a rather complete structural picture of the functional cycle of elongation factor‐Tu and especially of the elongation phase of protein biosynthesis. The discovery that three domains of elongation factor‐G are structurally mimicking the amino‐acylated tRNA in the ternary complex of elongation factor‐Tu has been the basis of much discussion of the functional similarities and functional differences of elongation factor‐Tu and elongation factor‐G in their interactions with the ribosome. Elongation factor‐G:GDP is now thought to leave the ribosome in a state ready for checking the codon‐anticodon interaction of the aminoacyl‐tRNA contained in the ternary complex of elongation factor‐Tu. Elongation factor‐G does this by mimicking the shape of the ternary complex. Other translation factors such as the initiation factor‐2 and the release factor 1 or 2 are also thought to mimic tRNA. These observations raise questions concerning the possible evolution of G‐proteins involved in protein biosynthesis.