The start codon is a specific sequence of three nucleotides (a codon) in messenger RNA (mRNA) that signals the ribosome where to begin translating the genetic code into a protein. The most common and standard start codon is AUG , which codes for the amino acid methionine in eukaryotes and archaea, and for N-formylmethionine (fMet) in bacteria, mitochondria, and plastids
. Key points about the start codon:
- It is always the first codon translated in an mRNA sequence by the ribosome
- AUG is the universal start codon, though rare alternative start codons exist in some organisms
- The start codon not only signals the beginning of translation but also establishes the reading frame for translating the rest of the mRNA into a protein
- In eukaryotes, AUG codes for methionine; in prokaryotes, it codes for formylmethionine
- The region before the start codon is called the 5' untranslated region (5' UTR)
In summary, the start codon (typically AUG) is essential for initiating protein synthesis and ensuring the correct translation of genetic information
