A ribosomal protein is required for translational regulation of GCN4 mRNA - Evidence for involvement of the ribosome in eIF2 recycling

In amino acid-starved yeast cells, inhibition of the guanine nucleotide exc hange factor eIF2B by phosphorylated translation initiation factor 2 result s in increased translation of GCN4 mRNA. We isolated a suppressor of a muta nt eIF2B. The suppressor prevents efficient GCN4 mRNA translation due to in activation of the small ribosomal subunit protein Rps31 and results in low amounts of mutant 40 S ribosomal subunits. Deletion of one of two genes enc oding ribosomal protein Rps17 also reduces the amounts of 40 S subunits but does not suppress eIF2B mutations or prevent efficient GCN4 translation. O ur findings show that Rps31-deficient ribosomes are altered in a way that d ecreases the eIF2B requirement and that the small ribosomal subunit mediate s the effects of low eIF2B activity on cell viability and translational reg ulation in response to eIF2 phosphorylation.