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tRNA fMet

Function and Interaction with mRNA

tRNA fMet is the tRNA used for the initiation of protein synthesis. Called an, "initiator protein," It is the fist tRNA molecule that enters the ribosome, specifically at the P site. This is in contrast to all other tRNAs which enter the A site. The amino acid attached to tRNA fMet is N-formylmethionine, which is the first amino acid assembled into the polypeptide chain during bacterial translation. N-formylmethionine attaches to tRNA fMet on its .

tRNA fMet and Ribosome Interaction

Like all tRNA molecules, tRNA fmet is composed of . Of these four stems, the loop of the tRNA fmet is critical to its function as it attaches to the "AUG" initiation codon on the mRNA, through base pairing, which has already been bound to the small subunit of the ribosome. This binding to the initiation codon requires initiation factor 2 (IF-2) and forms a complex with GTP. This complex is collectively referred to as the 30S initiation complex and is located within the cytoplasm of the cell. Then, as the ribosome translocates down the mRNA strand, additional tRNA molecules enter the ribosome with amino acids that bond with the N-formylmethionine previously attached to tRNA fMet. In this way, tRNA fMet is one of the molecules that begins the process of converting a genetic code to a protein.

Origination of tRNA fMet

tRNA fMet is present as the initiator tRNA only in bacteria, and not in eukaryotes or archaeans. Currently, the origin of tRNA fMet remains a mystery among scientists and geneticists. However, because of its presence in only one of the domains of life, there are two possible scenarios for the molecule's origin. It can be inferred that tRNA fMet originated in bacteria after archaeans diverged from bacteria, or that it was present in the common ancestor of bacteria and archaeans, and then archaeans lost the characteristic. tRNA Pro, tRNA Glu, and tRNA Thr all appear to be possible ancestors of the tRNA fMet molecule that is currently used as bacterial initiator tRNA. The reason for switching from these tRNAs to tRNA Met is unclear. Nonetheless, initiator tRNAs themselves are highly conserved across all domains of life, as they are crucial to protein synthesis.

References

Pierce, Benjamin A. Genetics: a conceptual approach. New York: Freeman, 2012. Print.

Bhattacharyya, Souvik. "Evolution of Initiator TRNAs and Selection of Methionine as the Initiating Amino Acid." Tandfonline. RNA Biology, 20 June 2016. Web. 08 Feb. 2017.

"TRNA." TRNA - Proteopedia, Life in 3D. N.p., n.d. Web. 08 Feb. 2017.