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→Reading frame: wikilinking Vertebrate mitochondrial code; small change in wording of AUG/ATG in RNA/DNA for clarity. |
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===Reading frame===
{{Main article|Reading frame}}
A reading frame is defined by the initial triplet of nucleotides from which translation starts. It sets the frame for a run of successive, non-overlapping codons, which is known as an "[[open reading frame]]" (ORF). For example, the string 5'-AAATGAACG-3' (see figure), if read from the first position, contains the codons AAA, TGA, and ACG ; if read from the second position, it contains the codons AAT and GAA ; and if read from the third position, it contains the codons ATG and AAC. Every sequence can, thus, be read in its [[5' to 3'|5' → 3' direction]] in three [[reading frames]], each producing a possibly distinct amino acid sequence: in the given example, Lys (K)-Trp (W)-Thr (T), Asn (N)-Glu (E), or Met (M)-Asn (N), respectively (when translating with the [[vertebrate mitochondrial code]]). When DNA is double-stranded, six possible [[reading frames]] are defined, three in the forward orientation on one strand and three reverse on the opposite strand.<ref name="genetics_ dictionary"/>{{rp|330}} Protein-coding frames are defined by a [[start codon]], usually the first AUG
In [[eukaryote]]s, ORFs in [[exon]]s are often interrupted by [[intron]]s.
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