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An open reading frame (ORF) is a reading frame that has the potential to be transcribed into RNA and translated into protein. It requires a continuous sequence of DNA which may include a start codon, through a subsequent region which has a length that is a multiple of 3 nucleotides, to a stop codon in the same reading frame.
The double helix of a DNA molecule has two anti-parallel strands; with the two strands having three reading frames each, there are six possible frame translations. [15] Example of a six-frame translation. The nucleotide sequence is shown in the middle with forward translations above and reverse translations below.
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 ...
This is known as the standard reading frame. However, in cases of frame shift mutations, an extra nucleotide (or more) is inserted into the DNA sequence, disrupting the typical reading frame and causing a shift in the sequence. This insertion prompts a shift in the reading frame due to the triplet nature of the genetic code.
Slippery sequences can potentially make the reading ribosome "slip" and skip a number of nucleotides (usually only 1) and read a completely different frame thereafter. In programmed −1 ribosomal frameshifting, the slippery sequence fits a X_XXY_YYH motif, where XXX is any three identical nucleotides (though some exceptions occur), YYY ...
For each nucleotide triplet (square brackets), the corresponding amino acid is given (one-letter code), either in the +1 reading frame for MT-ATP8 (in red) or in the +3 frame for MT-ATP6 (in blue). In this genomic region, the two genes overlap. The start codon is the first codon of a messenger RNA (mRNA) transcript translated by a ribosome.
Out-of-phase overlaps occurs when the shared sequences use different reading frames. This can occur in "phase 1" or "phase 2", depending on whether the reading frames are offset by 1 or 2 nucleotides. Because a codon is three nucleotides long, an offset of three nucleotides is an in-phase, phase 0 frame.
Whereas prokaryotic CDS predictors mostly deal with open reading frames (ORFs), which are segments of DNA between the start and stop codons, eukaryotic CDS predictors are faced with a more difficult problem because of the complex organization of eukaryotic genes. [3] CDS prediction methods can be classified into three broad categories: [2] [31]