You and your brother share the same eyes, but you and your sister have the same hair? Patterns of inheritance are complicated, and the microbial world is no exception. Take the archaea: since they’re small, we often assume they have more in common with bacteria than with eukaryotes. We even lump archaea and bacteria together in the not-quite-taxonomically-precise-category of “prokaryotes”. But the archaea represent their own unique domain in the tree of life, and conflating them with bacteria is a clear-cut case of sizeism that may eventually attract the attention of civil liberties lawyers.
A new study coming out in mBio this week shows that when it comes to DNA replication, archaea have more in common with their eukaryotic cousins than with bacteria. Li et al. started with 19 strains of the archaeon Thermococcus kodakarensis, each of which synthesizes a different His6-tagged protein component of the DNA replication machinery. By examining stable protein complexes in the replication machinery and identifying the proteins involved, the authors mapped the fishnet of interactions needed for an archaeon to copy its DNA. As the authors say, “The results confirmed and extend predictions from genome sequencing that the archaeal replication system is less complex but more closely related to a eukaryotic than to a bacterial replication system.”