Hans Amesz

The Control of the Rate of Initiation of Eukaryotic Protein Synthesis

Publisher Summary This chapter discusses the control of the rate of initiation of eukaryotic protein synthesis. Control of the rate of initiation of protein synthesis is manifested at many different occasions during the lifetime of an average eukaryotic cell. During the cell cycle, there is no initiation of protein synthesis in mitosis. In the late S phase and in G2 phase, a gradual diminishing of initiation occurs. Under physiological stress—such as serum deprivation, amino-acid starvation, and hyperthermic treatment—the initiation rate is lowered substantially. The model for the control of the rate of initiation implies that when a complex is formed between eIF-2 and eRF, a high rate of initiation is achieved, whereas conditions that impair complex formation inevitably cause a low initiation rate. Reduced eIF-2 displays a much higher activity in lysate systems than oxidized eIF-2.

Postribosomal complexes containing eukaryotic initiation factor eIF-2

Eukaryotic initiation factors are found in the postribosomal supernatant as well as bound to the 40S ribosomal subunits. We have analyzed the factor activities from the supernatant by means of zonal centrifugation followed by Sepharose-heparin affinity chromatography. They exist both as free factors, sedimenting in a broad range from 4 to 7S, and complexed with other protein(s) with a sedimentation value of 16–20S. This complexed fraction contains besides eIF-2 another activity which exhibits a profound stimulation on amino acid incorporation in crude lysates and appears to counteract the heme-regulated inhibitor.