The nucleotide triplet AUG serves as the initiation signal for protein synthesis in most organisms. This codon directs the ribosome to begin translating messenger RNA (mRNA) and establishes the reading frame for subsequent codons. In eukaryotes, AUG typically codes for methionine; in prokaryotes, it codes for N-formylmethionine. This specificity ensures the accurate construction of polypeptide chains, beginning with the designated amino acid.
The precise start signal is vital because it dictates which region of the mRNA will be translated into protein. Errors in start site selection can lead to truncated proteins, proteins with altered function, or complete failure of protein production. The fidelity of this initiation step is therefore crucial for cellular function and viability. Historically, the identification of this signal was a pivotal step in understanding the central dogma of molecular biology and how genetic information is translated into functional proteins.
