Terminating eukaryote translation: Domain 1 of release factor eRF1 functions in stop codon recognition

Eukaryote ribosomal translation is terminated when release factor eRF1, in a complex with eRF3, binds to one of the three stop codons. The tertiary st ructure and dimensions of eRF1 are similar to that of a tRNA, supporting th e hypothesis that release factors may act as molecular mimics of tRNAs, To identify the yeast eRF1 stop codon recognition domain (analogous to a tRNA anticodon), a genetic screen was performed to select for mutants with disab led recognition of only one of the three stop codons, Nine out of ten mutat ions isolated map to conserved residues within the eRF1 N-terminal domain 1 .A subset of these mutants, although wild-type for ribosome and eRF3 intera ction, differ in their respective abilities to recognize each of the three stop codons, indicating codon-specific discrimination defects, Five of six of these stop codon-specific mutants define yeast domain 1 residues (I32, M 48, V68, L123, and H129) that locate at three pockets on the eRF1 domain 1 molecular surface into which a stop codon can be modeled. The genetic scree n results and the mutant phenotypes are therefore consistent with a role fo r domain 1 in stop codon recognition; the topology of this eRF1 domain, tog ether with eRF1-stop codon complex modeling further supports the proposal t hat this domain may represent the site of stop codon binding itself.