fMettRNAiMet

fMettRNAiMet, also known as formylmethionyl-tRNAiMet, is a crucial initiator tRNA molecule in prokaryotes and mitochondria. Its primary role is to carry the modified amino acid N-formylmethionine (fMet) to the ribosome to initiate protein synthesis. Unlike regular methionyl-tRNA (Met-tRNA), which can be used for internal methionine incorporation, fMettRNAiMet is specifically recognized by the translation initiation factors to start the polypeptide chain.

The N-formyl group on methionine is essential for this initiation function. In bacteria, the formylation of methionine on the initiator tRNA is catalyzed by a specific enzyme called methionine transformylase. This formyl group is later removed by a deformylase enzyme once the polypeptide chain has been sufficiently elongated. The fMet residue is either removed or remains at the N-terminus of the mature protein, depending on the specific protein sequence and cellular processing mechanisms.

The structural distinction between the initiator tRNA (tRNAiMet) and the elongator tRNA (tRNAMet) is critical for the fidelity of translation initiation. This specificity ensures that protein synthesis begins at the correct start codon, typically AUG. The presence and function of fMettRNAiMet are therefore fundamental to the process of gene expression in organisms that utilize this formylated initiator.