Open reading frame

<p>In <a href="/facts/Molecular_biology/YgqU35ub">molecular biology</a>, reading frames are defined as spans of <a href="/facts/DNA/nB89Iauz">DNA</a> sequence between the start and stop <a href="/facts/Codon/zUK0bY1B">codons</a>. Usually, this is considered within a studied region of a <a href="/facts/Prokaryote/oYyvaDDH">prokaryotic</a> DNA sequence, where only one of the six possible reading frames will be "open" (the "reading", however, refers to the RNA produced by <a href="/facts/Transcription_(biology)/bDgp9HDN">transcription</a> of the DNA and its subsequent interaction with the <a href="/facts/Ribosome/CF2u2gtg">ribosome</a> in <a href="/facts/Translation_(biology)/JcPC1rth">translation</a>). Such an open reading frame (ORF) may contain a <a href="/facts/Start_codon/Rn2L6gXQ">start codon</a> (usually AUG in terms of <a href="/facts/RNA/HxPeNfNj">RNA</a>) and by definition cannot extend beyond a <a href="/facts/Stop_codon/1yuAkq9X">stop codon</a> (usually UAA, UAG or UGA in RNA). That start codon (not necessarily the first) indicates where translation may start. The <a href="/facts/Transcription_terminator/mdR46gBa">transcription termination</a> site is located after the ORF, beyond the translation stop codon. If transcription were to cease before the stop codon, an incomplete <a href="/facts/Protein/Jxmagu3E">protein</a> would be made during translation.
</p><p>In <a href="/facts/Eukaryote/SkwyPLMA">eukaryotic</a> <a href="/facts/Gene/e1swwPY6">genes</a> with multiple <a href="/facts/Exon/8KWJtLuN">exons</a>, <a href="/facts/Intron/LS6YdBEK">introns</a> are removed and exons are then joined together after transcription to yield the final <a href="/facts/MRNA/oUL6qxQn">mRNA</a> for protein translation. In the context of <a href="/facts/Gene_prediction/QFdMeIN2">gene finding</a>, the start-stop <a href="/facts/Definition/5SlGKKDJ">definition</a> of an ORF therefore only applies to spliced <a href="/facts/Messenger_RNA/oUL6qxQn">mRNAs</a>, not genomic DNA, since introns may contain stop codons and/or cause shifts between reading frames. An alternative definition says that an ORF is a sequence that has a length divisible by three and is bounded by stop codons. This more general definition can be useful in the context of <a href="/facts/Transcriptomics_technologies/0ytdk54p">transcriptomics</a> and <a href="/facts/Metagenomics/GWFeMd7z">metagenomics</a>, where a start or stop codon may not be present in the obtained sequences. Such an ORF corresponds to parts of a gene rather than the complete gene.
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Open reading frame open-in-new

Open reading frame