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. 1970 Dec;67(4):1681–1687. doi: 10.1073/pnas.67.4.1681

Protein Chain Initiation by Methionyl-tRNA in Wheat Embryo*

Abraham Marcus 1,2, Donald P Weeks 1,2, Jonathan P Leis 1,2, Elizabeth B Keller 1,2
PMCID: PMC283412  PMID: 5275369

Abstract

The mechanism of protein chain initiation has been investigated in a cell-free amino acid incorporation system from wheat embryos dependent on tobacco mosaic virus RNA. Analysis of the N-termini of the labeled peptide products of short-term incubations showed the presence of unblocked methionine. In addition, methionyl-tRNA (Met-tRNA) could be bound to ribosomes at 1.3 mM Mg++ in a reaction requiring viral RNA, ATP, GTP, and soluble protein factors.

Incorporation experiments with the two cytoplasmic Met-tRNAs of wheat germ, an initiating species designated Met-tRNAi and a Met-tRNAm, showed that methionine transfer from Met-tRNAi was linear from zero time, while that from Met-tRNAm occurred only after an appreciable lag. Analysis of the peptide products showed that methionine transfer from Met-tRNAi was predominantly N-terminal. In contrast, methionine transfer from Met-tRNAm was exclusively into internal positions. Similar selectivity was observed in the ribosome binding assay; only Met-tRNAi showed a strong reaction. These experiments provide strong evidence that in the wheat embryo, cytoplasmic Met-tRNAi functions without formylation in the initiation of protein synthesis.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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