Biochem Genet. 2025 Dec 29.
In Saccharomyces cerevisiae, the AUG codon typically signals translation initiation to set an open reading frame, with a preference for the A- 3AA/U- 1(AUG)U+ 4 sequence context. The mutant eIF5G31R or eIF2βS264Y proteins cause translation initiation fidelity defect by initiating translation at a near cognate UUG codon, in addition to the AUG start codon (suppressor of initiation codon; Sui¯ phenotype). However, the critical role of the - 3 to - 1 sequences in selecting the UUG start codon by these Sui¯ mutants is not fully explored. Different HIS4UUG-LacZ reporter constructs were made with UUG as the start codon and varied nucleotides at the - 3 and - 2 positions or individually at -1 positions. These constructs were transformed to yeast cells having eIF5G31R or eIF2βS264Y mutation, and the β-galactosidase activity was measured. The HIS4UUG-LacZ transcripts carrying a purine (A/G) at the - 3 position showed higher reporter activity than those with a pyrimidine (U/C). Additionally, purines were favored at the - 1 position within an AA (- 3 and - 2) context for efficient UUG start codon selection. Our findings demonstrate that UUG start codon recognition by Sui¯ mutants eIF5G31R and eIF2βS264Y is greatly influenced by the surrounding nucleotide context, each showing distinct context preferences. This highlights the nuanced role of sequence context in the near-cognate UUG codon initiation by the Sui¯ mutants.
Keywords: Sequence context; Start codon selection; Sui¯ phenotype; Translation initiation; eIF2β; eIF5