40S subunit X Met-tRNAf complexes and initiation factor eIF-2 phosphorylation in mammalian cells accumulating uncharged tRNA.

A significant, reversible decline in the level of 40S subunit X Met-tRNAf complexes was observed in HeLa cells treated with either of two inhibitors of tRNA charging, histidinol or O-methylthreonine. A decline in 40S X subunit Met-tRNAf complexes was also seen in HeLa cells deprived of histidine and in mutant Chinese hamster ovary cells, bearing a temperature-sensitive leucyl-tRNA charging enzyme, when they were incubated at a non-permissive temperature. Treatment with histidinol or O-methylthreonine did not affect the relative degree of phosphorylation of the alpha subunit of initiation factor eIF-2. Histidinol did not stimulate the activity of the endogenous kinase for eIF-2 alpha subunit in extracts prepared from HeLa cells. In the presence of histidinol the phosphorylation level of a 25000-dalton protein was reversibly increased.