Reading frame

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In biology, a reading frame is a contiguous and non-overlapping set of three-nucleotide codons in DNA or RNA. There are 3 possible reading frames in a mRNA strand and six in a double stranded DNA molecule. This leads to the possibility of overlapping genes and there may be many of these in bacteria.<ref name=Johnson_2004>Johnson Z, Chisholm S (2004). "Properties of overlapping genes are conserved across microbial genomes.". Genome Res 14 (11): 2268-72. PMID 15520290.</ref> Some viruses e.g. HBV and BYDV use several overlapping genes in different reading frames.

In rare cases a translating ribosome may shift from one frame to another, a translational frameshift. It is distinct from a frameshift mutation as the nucleotide sequence (DNA or RNA) is not altered only the frame in which it is read.

A reading frame that contains a start codon and a stop codon is called an open reading frame (ORF).