Initiation codon

Initiation codon or start codon is a specific nucleotide triplet in mRNA that signals the start of translation. It is the first codon of a messenger RNA (mRNA) transcript translated by a ribosome. In eukaryotes and Archaea, the amino acid encoded by the start codon is always methionine. The most common start codon is AUG.

Function

The initiation codon plays a crucial role in protein synthesis. It not only signifies the start of a protein coding sequence but also sets the reading frame for the ribosome, thus influencing the entire translation process.

Recognition

The recognition of the initiation codon is mediated by initiation factors, which in eukaryotes includes eIF2 and eIF5. These factors help the ribosome to identify the start codon and initiate protein synthesis.

Variations

While AUG is the most common initiation codon, certain organisms and mitochondrial genomes may use alternative start codons. For example, the yeast Saccharomyces cerevisiae can use the codon CUG as a start codon, while certain viruses can use GUG or UUG.

See also

• Genetic code
• Translation (biology)
• Stop codon
• Codon