Increased competition for eIF4 factors or 40S ribosomal subunits disfavors translation preinitiation complex assembly on poorly translated mRNAs with high G/A nucleotide ratios in 5’ leaders

ABSTRACT: The ribosome concentration model (RCM) posits that reducing the concentration of ribosomal subunits re-programs translation initiation to favor mRNAs with high rates of 48S preinitiation complex (PIC) assembly over mRNAs with low assembly rates. We tested the RCM using the yeast reconstituted initiation system by measuring PIC assembly on all native mRNAs in parallel (Rec-Seq) at different 40S subunit concentrations. We found broad agreement with the RCM, as mRNAs with the largest decreases in PIC assembly when 40S subunits became limiting tend to be the least efficient in PIC assembly at the lowest [40S]/[mRNA] ratio. Likewise, reductions in PIC assembly at limiting 40S in Rec-Seq correlated with translational efficiencies (TE) of mRNAs in WT yeast determined by ribosome profiling (Ribo-Seq). Conclusions in line with the RCM also emerged from Rec-Seq conducted in the absence or presence of mRNA-recruitment factors eIF4E-eIF4G or eIF4B and by Ribo-Seq analysis of a tif3Δ mutant lacking eIF4B, wherein mRNAs least efficient for PIC assembly or translation in absence of the factor generally showed the greatest impairment when it is missing . Remarkably, occurrence of G nucleotides in 5’UTRs is associated with low PIC assembly and TE in vivo and confers heightened sensitivity to limiting 40S, eIF4E-eIF4G, eIF4B or eIF4A in Rec-Seq reactions, and to the elimination/depletion of eIF4B and eIF4E in vivo. We speculate that G residues impede processive ribosomal scanning in a manner overcome by eIF4 factors and high rates of 43S PIC attachment at mRNA 5’ ends.

ORGANISM(S): Saccharomyces cerevisiae Saccharomyces cerevisiae BY4741

PROVIDER: GSE309137 | GEO | 2026/04/13

REPOSITORIES: GEO