Possible evolution of factors involved in protein biosynthesis

The elongation factors of protein biosynthesis are well preserved through o ut evolution. They catalyze the elongation phase of protein biosynthesis, w here on the ribosome amino acids are added one at a time to a growing pepti de according to the genetic information transcribed into mRNA. Elongation f actor Tu (EF-Tu) provides the binding of aminoacylated tRNA to the ribosome and protects the aminoester bond against hydrolysis until a correct match between the codon on mRNA and the anticodon on tRNA can be achieved. Elonga tion factor G(EF-G) supports the translocation of tRNAs and of mRNA on the ribosome so that a new codon can be exposed for decoding. Both these factor s are GTP binding proteins, and as such exist in an active form with GTP an d an inactive form with GDP bound to the nucleotide binding domain. Elongat ion factor Ts (EF-Ts) will catalyze the exchange of nucleotide on EF-Tu. Th is review describes structural work on EF-Tu performed in our laboratory ov er the last eight years. The structural results provide a rather complete p icture of the major structural forms of EF-Tu, including the so called tern ary complex of aatRNA:EF-Tu:GTP. The structural comparison of this ternary complex with the structure of EF-G:GDP displays an unexpected macromolecula r mimicry, where three domains of EF-G mimick the shape of the tRNA in the ternary complex. This observation has initiated much speculation on the evo lution of all factors involved in protein synthesis, as well as on the deta ils of the ribosomal function in one part of elongation.