MettRNAMet

MettRNAMet is a designation used in some genomic annotations to denote the transfer RNA gene that encodes the aminoacylated tRNA for methionine, commonly referred to as tRNA^Met. This tRNA delivers methionine to the ribosome during protein synthesis and is charged with methionine by methionyl-tRNA synthetase. The mature molecule typically preserves the canonical tRNA cloverleaf structure and features an anticodon loop that reads the start codon AUG; in many organisms this anticodon is CAU, enabling recognition of AUG codons both at initiation and within elongating polypeptide chains. Sequence length and exact sequence context vary across species, but most tRNA^Met molecules are on the order of 70 to 75 nucleotides and undergo posttranscriptional modifications that stabilize folding and optimize decoding.

Localization and genetic organization of MettRNAMet can differ. In many eukaryotes, the gene is encoded in the nuclear genome and transcribed in the nucleus, with the tRNA subsequently imported into organelles as needed. In mitochondria or chloroplasts, a dedicated tRNA^Met gene is often encoded directly within the organellar genome, reflecting the compact, organelle-specific translation system. In these compartments, tRNA^Met frequently serves as the initiating tRNA for translation, facilitated by compartment-specific initiation factors.

Functional significance includes supplying methionine for initiation and internal placements of methionine during protein synthesis. Mutations or structural defects in MettRNAMet or its organellar copies can impair mitochondrial or chloroplast translation, contributing to respiratory or metabolic disorders in some organisms. MettRNAMet remains a focus in studies of tRNA biology, translation initiation, and organellar gene expression.