Bacterial and eukaryotic systems collide in the three Rs of Methanococcus.

Methanococcus maripaludis S2 is a methanogenic archaeon with a well-developed genetic system. Its mesophilic nature offers a simple system in which to perform complementation using bacterial and eukaryotic genes. Although information-processing systems in archaea are generally more similar to those in eukaryotes than those in bacteria, the order Methanococcales has a unique complement of DNA replication proteins, with multiple MCM (minichromosome maintenance) proteins and no obvious originbinding protein. A search for homologues of recombination and repair proteins in M. maripaludis has revealed a mixture of bacterial, eukaryotic and some archaeal-specific homologues. Some repair pathways appear to be completely absent, but it is possible that archaeal-specific proteins could carry out these functions. The replication, recombination and repair systems in M. maripaludis are an interesting mixture of eukaryotic and bacterial homologues and could provide a system for uncovering novel interactions between proteins from different domains of life.