Why endosymbionts rule - see #PLoS Genetics paper on origin of an alternative genetic code

Way way way cool new paper in PLoS Genetics from Nancy Moran's lab. The paper (Origin of an Alternative Genetic Code in the Extremely Small and GC–Rich Genome of a Bacterial Symbiont). The paper discusses the use of genome sequencing and proteomics (as well as a variety of bioinformatic analyses) of a bacterial symbiont (Hodgkinia) of cicadas.

And for those not in the know, this is an Open Access paper using a broad Creative Commons license (since it is in a PLoS journal) so anyone can reuse material from it as long as the source is cited. This image to the left is from their paper so I am citing the source here: McCutcheon JP, McDonald BR, Moran NA (2009) Origin of an Alternative Genetic Code in the Extremely Small and GC–Rich Genome of a Bacterial Symbiont. PLoS Genet 5(7): e1000565. doi:10.1371/journal.pgen.1000565

The study has some interesting things including:

• the genome of the symbiont has a much higher GC content than other small bacterial genomes for which the sequence is available
• the symbiont is member of the alpha proteobacterial group, which is somewhat unusual since most other insect endosymbionts that have been studied are from the gamma proteobacterial group and/or the bacteroidetes clade
• the UGA codon in this species is used to encode tryptophan and not as a stop codon

Taken together these things are very interesting since other species that have been found to have the UGA codon reassigned to code for an amino acid all have low genomic GC content. This correlation led people to conclude that the codon reassignment was directly related to the low GC content. However, the authors suggest here that the UGA reassignment in many species might be due to the genome reduction (loss of genes) seen in endosymbionts and not to low GC content.

Anyway the paper is worth a read ...


McCutcheon, J., McDonald, B., & Moran, N. (2009). Origin of an Alternative Genetic Code in the Extremely Small and GC–Rich Genome of a Bacterial Symbiont PLoS Genetics, 5 (7) DOI: 10.1371/journal.pgen.1000565