The secret code behind the genetic code. Well...

A second code hiding in the DNA?

"Scientists have discovered a second code hiding within DNA". That's the headline about the results of a study published today in the journal Science. It shows that 15% of the codons in humans have a dual function: the traditional coding of amino acids and, that’s the novelty, the control of gene expression. Those dual codons were dubbed duons.

The genetic code allows to convert the alphabet of codons (triplets of nucleic acid) to single amino acids. This code is actually redundant and up to six codons can be used to code a unique amino acid. What's interesting is that genomes display a codon bias: one codon of the many possible ones is usually over-represented. Why this is happening is a good question and the study published today is addressing it. What the study shows is that codon bias seems to correlated with the binding of transcription factors, those proteins that regulate gene expression.

Now, the genetic code is probably the only true code that does what a code is supposed to do, that is converting something into something else - in that case triplets of nucleic acid into single amino acids. So, talking about a second code is probably premature, although that wouldn't be the first time it happens. What the many tentative codes out there are really trying to address is the conversion of something into a process, either the regulation of gene expression or the modulation of protein activity. That's a rather complex task and the still elusive epigenetic code about the association of methylation or acetylation of histones to regulate gene expression would be a good example of this. I suppose this codes are the holy grails of biology, which is reminiscent of the unifying theories in physics.

The work reported in this study is nonetheless extremely interesting, and for certain, duon is going to be a buzzword in many labs and university hallways for some time. But enough with that. Now, let’s play my favourite game. Let’s try to guess what's going to be the next big mechanism that controls gene expression. Hint: why do the TFs bind to specific codons and not to others?

This study was published in Science by Stergachis et al, 2013.