Stimulation of protein synthesis and Met-tRNA binding by phosphorylated sugars: studies of their mechanism of action

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Abstract
Certain phosphorylated sugars stimulate protein synthesis in extracts of mammalian cells [rabbit reticulocyte lysates]. The effect was due to a stimulation of Met-tRNAf binding to 40S ribosomal subunits, both in whole extracts and with isolated ribosomes. Formation of a ternary complex of Met-tRNAf, initiation factor eIF-2, and GTP was not stimulated. The stimulation is not due solely to metabolism of the sugars. The present studies show that sugars prevent the inactivation of ribosomes that occurs during protein synthesis incubations. The sugars also inhibit cyclicAMP-dependent protein kinases noncompetitively. They stimulate Met-tRNAf binding to 40S ribosomal subunits even under conditions in which an inhibition of protein kinase has no effect. Although it has not been possible to demonstrate a direct association of the sugars with the 40S initiation complex, the evidence suggest that their effect is mediated by an interaction with one of the components in the formation of this complex.