In Saccharomyces cerevisiae, the AUG codon typically signals translation initiation to set an open reading frame, with a preference for the A^{- 3}AA/U^{- 1}(AUG)U^{+ 4} sequence context. The mutant eIF5^G31R or eIF2β^S264Y 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 HIS4^UUG-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 eIF5^G31R or eIF2β^S264Y mutation, and the β-galactosidase activity was measured. The HIS4^UUG-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 eIF5^G31R and eIF2β^S264Y 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.

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Journal Article

Authors

Ram AK, Kole T, Alone PV

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