Special peptidyl-tRNA molecules can promote translational frameshifting without slippage.
Recently we described an unusual programmed +1 frameshift event in yeast retrotransposon Ty3. Frameshifting depends on the presence of peptidyl-tRNA(AlaCGC) on the GCG codon in the ribosomal P site and on a translational pause stimulated by the slowly decoded AGU codon. Frameshifting occurs on the sequence GCG-AGU-U by out-of-frame binding of a valyl-tRNA to GUU without slippage of peptidyl-tRNA(AlaCGC). This mechanism challenges the conventional understanding that frameshift efficiency must correlate with the ability of mRNA-bound tRNA to slip between cognate or near-cognate codons. Though frameshifting does not require slippery tRNAs, it does require special peptidyl-tRNAs. We show that overproducing a second isoacceptor whose anticodon had been changed to CGC eliminated frameshifting; peptidyl-tRNA(AlaCGC) must have a special capacity to induce +1 frameshifting in the adjacent ribosomal A site. In order to identify other special peptidyl-tRNAs, we tested the ability of each of the other 63 codons to replace GCG in the P site. We found no correlation between the ability to stimulate +1 frameshifting and the ability of the cognate tRNA to slip on the mRNA--several codons predicted to slip efficiently do not stimulate frameshifting, while several predicted not to slip do stimulate frameshifting. By inducing a severe translational pause, we identified eight tRNAs capable of inducing measurable +1 frameshifting, only four of which are predicted to slip on the mRNA. We conclude that in Saccharomyces cerevisiae, special peptidyl-tRNAs can induce frameshifting dependent on some characteristic(s) other than the ability to slip on the mRNA.
Department of Biological Sciences, University of Maryland, Baltimore 21228.
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Vimaladithan
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Farabaugh
D000926:Anticodon; D001483:Base Sequence; D003062:Codon; D004251:DNA Transposable Elements; D016368:Frameshift Mutation; D015966:Gene Expression Regulation, Fungal; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D012331:RNA, Fungal / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D012343:RNA, Transfer / Q000378:metabolism*; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism*
D000926:Anticodon; D003062:Codon; D004251:DNA Transposable Elements; D012331:RNA, Fungal; D012333:RNA, Messenger; D012346:RNA, Transfer, Amino Acyl; C019037:tRNA, peptidyl-; D012343:RNA, Transfer