Ribosomal mutation in helix 32 of 18S rRNA alters fidelity of eukaryotic translation start site selection.

The 40S ribosome plays a critical role in start codon selection. To gain insights into the role of its 18S rRNA in start codon selection, a suppressor screen was performed that suppressed the preferential UUG start codon recognition (Suppressor of initiation codon: Sui- phenotype) associated with the eIF5G31R mutant. The C1209U mutation in helix h32 of 18S rRNA was found to suppress the Sui- and Gcn- (failure to derepress GCN4 expression) phenotype of the eIF5G31R mutant. The C1209U mutation suppressed Sui- and Gcd- (constitutive derepression of GCN4 expression) phenotype of eIF2βS264Y , eIF1K60E , and eIF1A-ΔC mutation. We propose that the C1209U mutation in 40S ribosomal may perturb the premature head rotation in 'Closed/PIN ' state and enhance the stringency of translation start site selection.