start codon

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start codon (initiation codon) The triplet of nucleotides on a messenger RNA molecule (see codon) at which the process of translation is initiated. In eukaryotes the start codon is AUG (see genetic code), which codes for the amino acid methionine; in bacteria the start codon can be either AUG, coding for N-formyl methionine, or GUG, coding for valine. Compare stop codon.