Division of RNA/DNA sequences into sets of triplets which correspond to amino acids
In
codons
.
A single strand of a
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.[1][2]
In general, at the 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. There is one known example of overlapping reading frames in mammalian mitochondrial DNA: coding portions of genes for 2 subunits of ATPase overlap.
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.[4]
When a putative amino acid sequence resulting from the translation of an ORF remained unknown in mitochondrial and chloroplast genomes, the corresponding open reading frame was called an unidentified reading frame (URF). For example, the
The usage of multiple reading frames leads to the possibility of
BYDV
, use several overlapping genes in different reading frames.
In rare cases, a ribosome may shift from one frame to another during translation of an mRNA (
translational frameshift). This causes the first part of the mRNA to be translated in one reading frame, and the latter part to be translated in a different reading frame. This is distinct from a frameshift mutation
, as the nucleotide sequence (DNA or RNA) is not altered—only the frame in which it is read.