It may come as a surprise to many but Drosophila melanogaster, the common fruit vinegar fly, is almost as abundant in genetics labs as it is in your compost pail. And I’m not just talking about the lunch fridge. Drosophila has been an invaluable model organism for genetics and developmental biology research for over a century.

Its relatively tractable genome size (165 million base pairs) and importance in the research community led to its genome being sequenced early in the genomics era. The genomics company Celera famously accomplished this in 2000 as a warm-up to their human sequencing run. The assembled genome was a massively useful resource for the research community (including obscure grad students toiling in search of obscure genes).

At a later date (2007 perhaps?) an additional 11 species of Drosophila were sequenced. This set of 12 genomes has been useful for comparative analysis of these species, looking for differences in the genomes that have arisen since these species diverged. An interesting analysis from this dataset arrived inGenome Research earlier this week. [Paper link below – it’s Open Access!]

The authors looked at conservation of gene sequences between the genomes and noticed something unexpected. The DNA sequences of the genes are expected to be slightly different, with species more distantly-related having more differences, and this is what you see. The proteins that the genes encode, however, have to retain their function and so there are some limits on how much they can vary. So, what you would expect is that the protein-coding portions of the genes would display these constraints but the non-protein-coding portions of the genes would not. This is what is observed for most genes, but not all of them. In 283 genes, the sequence following the stop codon (where the protein should end) continued to show the functional constraints. This results suggests that in these genes the ribosome will sometimes disregard the stop codon and continue to add to the protein. And these additional sequences were conserved between species further suggesting that the extended proteins confer some sort of selective advantage.

On our morning walks to school I am always reminding my daughter that many drivers will see Stop signs but think they say “slow down a bit”. Now I’ll have to include ribosomes in my lectures too.

http://genome.cshlp.org/content/21/12/2096.full