Translational frameshifting or
ribosomal frameshifting refers to an alternative process of
protein translation. A protein is translated from one end of the
mRNA to the other, from the 5' to the 3' end. Normally a protein is translated from a template mRNA with consecutive blocks of 3
nucleotides being read as single amino acids. However, certain organisms may exhibit a change or shift in the
ribosomes frame by one or two nucleotides when translating the
genetic code. This is deemed translational or ribosomal frameshifting. The process can be programmed by the
nucleotide sequence of the
mRNA and is sometimes affected by the secondary or tertiary mRNA structure. It has been described mainly in
viruses (especially
retroviruses),
retrotransposons and bacterial insertion elements, and also in some cellular genes.