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reading frame
In molecular biology, a reading frame is a way of dividing the sequence of nucleotides in a nucleic acid (DNA or RNA) molecule into a set of consecutive, non-overlapping triplets. Where these triplets equate to amino acids or stop signals during translation, they are called codons.
A single strand of a nucleic acid molecule has a phosphoryl end, called the 5′-end, and a hydroxyl or 3′-end. These define the 5'→3' direction. There are three reading frames that can be read in this 5'→3' direction, each beginning from a different nucleotide in a triplet. In a double stranded nucleic acid, an additional three reading frames may be read from the other, complementary strand in the 5'→3' direction along this strand. As the two strands of a double stranded nucleic acid molecule are antiparallel, the 5'→3' direction on the second strand corresponds to the 3'→5' direction along the first strand.
In general, at most one reading frame in a given section of a nucleic acid is biologically relevant (open reading frame). Some viral transcripts can be translated using multiple, overlapping reading frames.〔(【引用サイトリンク】first=Eric )〕 There is one example of overlapping reading frames in mammalian mitochondrial DNA: coding portions of genes for 2 subunits of ATPase overlap.
== Genetic code ==
(詳細はcodons. Any given sequence of DNA can therefore be read in six different ways: Three reading frames in one direction (starting at different nucleotides) and three in the opposite direction. During transcription, the RNA polymerase read the template DNA strand in the 3'→5' direction, but the mRNA is formed in the 5' to 3' direction, however. The mRNA is single-stranded and therefore only contains three possible reading frames, of which only one is translated. The codons of the mRNA reading frame are translated in the 5'→3' direction into amino acids by a ribosome to produce a polypeptide chain.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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