Protein-coding genes provide a sequence of nucleotides that is read three nucleotides at a time. Each triplet is translated into a particular type of amino acid. So a sequence of 300 nucleotides codes for 100 amino acids, which are attached to each other to make a protein. But what if you started not with the first nucleotide in the sequence, but with the second one? You would have a different sequence of nucleotide triplets, and so a different sequence of amino acids. This is also true if you started with the third nucleotide. In fact you could switch over to the opposing DNA strand (the other half of the double helix) and again you would have the choice between three different “frames,” resulting in three different sequences of amino acids. So in all you can choose between six different reading frames. So any given gene has the theoretical possibility of containing different genetic messages, in the different reading frames. And indeed, years ago it was discovered that genes are overlapping—portions of their nucleotide sequence exist on the same segment of DNA, just in a different reading frame. But an even more bizarre theoretical possibility is that the reading frame could shift while the sequence of nucleotides is being read. In that case you are mixing and matching partial sequences from different reading frames. Now, a new studyhas investigated this capability and discovered a fascinating mechanism that apparently enables the real-time frame shifting. Read more