Reading frames

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 due to the two strands from which transcription is possible. This leads to the possibility of overlapping genes and there may be many of these in bacteria. 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.

An open reading frame (ORF) is a reading frame that contains a start codon and the subsequent translated region, but no stop codon.