Gene expression, translation and the behavior of proteins / edited by David M. Prescott, Lester Goldstein.

Date:
1980
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Gene expression, translation and the behavior of proteins / edited by David M. Prescott, Lester Goldstein. Source: Wellcome Collection.

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    54 John W. В. Hershey mutations are in the genes for ribosomal proteins S4, S5, and S12, but the precise effects in the molecular interactions discussed above are not known. A kinetic analysis of missense and nonsense suppression with these mutants has been made (Ninio, 1974). It is clear that great accuracy is required for the synthesis of active enzymes. The cell must, therefore, balance its need for such accuracy against its need for rapid protein syn¬ thesis. C. The Termination Pathway Termination of protein synthesis results in hydrolysis of the completed peptide from its tRNA, followed by release from the ribosome of the peptide, its tRNA and the mRNA. The process begins with the peptidyl- tRNA in the P site [intermediate I or V (Fig. 8)] and one of the three nonsense codons, UAA, UAG, or UGA, in the A site. This configuration is recognized by the appropriate release factor, which binds to the ribo¬ some. In eukaryotic cells, RF binding requires OTP; in bacterial cells it does not. In cells containing a suppressor tRNA which can recognize the termination codon, the suppressor tRNA and the release factor compete for binding to the ribosome. The presence of RF on the ribosome activates the peptidyltransferase center, which transfers the peptidyl moiety to water. The various macromolecules then dissociate from the ribosome. The release of RF is stimulated by OTP hydrolysis in eukaryotic cells. The termination process in bacterial cells differs little from that in mammalian cells. Prokaryotic cells contain two codon-specific RF's, whereas mammalian cells contain one factor which recognizes all three nonsense codons. GTP is involved in eukaryotic cells, but may also be involved in the function of RF-3 in prokaryotes. The interaction of bacte¬ rial RF's with ribosomes has been studied in some detail. The RF's inter¬ act with ribosomal proteins L7/L12 and S9 and are prevented from binding by prebound EF-G or EF-Tu. The nature of the molecular interactions of RF with the nonsense codons or with the peptidyltransferase center is unclear. A recent review of the details of the termination process in pro¬ karyotic and eukaryotic cells is available (Caskey, 1977). V. PERSPECTIVES This review describes the impressive amounts of new knowledge gener¬ ated over the past 20 years by studies of protein synthesis in both pro¬ karyotic and eukaryotic cells. Progress has been somewhat more rapid
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