DNA replication in the archaea.

The archaeal DNA replication machinery bears striking similarity to that of eukaryotes and is clearly distinct from the bacterial apparatus. In recent years, considerable advances have been made in understanding the biochemistry of the archaeal replication proteins. Furthermore, a number of structures have now been obtained for individual components and higher-order assemblies of archaeal replication factors, yielding important insights into the mechanisms of DNA replication in both archaea and eukaryotes.     

DNA Replication in the Archaea

The archaeal DNA replication machinery bears striking similarity to that of eukaryotes and is clearly distinct from the bacterial apparatus. In recent years, considerable advances have been made in understanding the biochemistry of the archaeal replication proteins. Furthermore, a number of structures have now been obtained for individual components and higher-order assemblies of archaeal replication factors, yielding important insights into the mechanisms of DNA replication in both archaea and eukaryotes.     

The archaeal Sec-dependent protein translocation pathway

Over the past three decades, transport of proteins across cellular membranes has been studied extensively in various model systems. One of the major transport routes, the so-called Sec pathway, is conserved in all domains of life. Very little is known about this pathway in the third domain of life, archaea. The core components of the archaeal, bacterial and eucaryal Sec machinery are similar, although the archaeal components appear more closely related to their eucaryal counterparts. Interestingly, the accessory factors of the translocation machinery are similar to bacterial components, which indicates a unique hybrid nature of the archaeal translocase complex. The mechanism of protein translocation in archaea is completely unknown. Based on genomic sequencing data, the most likely system for archaeal protein translocation is similar to the eucaryal co-translational translocation pathway for protein import into the endoplasmic reticulum, in which a protein is pushed across the translocation channel by the ribosome. However, other models can also be envisaged, such as a bacterial-like system in which a protein is translocated post-translationally with the aid of a motor protein analogous to the bacterial ATPase SecA. This review discusses the different models. Furthermore, an overview is given of some of the other components that may be involved in the protein translocation process, such as those required for protein targeting, folding and post-translational modification.     

FtsZ-less cell division in archaea and bacteria

A dedicated cell division machinery is needed for efficient proliferation of an organism. The eukaryotic actin-myosin based mechanism and the bacterial FtsZ-dependent machinery have both been characterized in detail, and a third division mechanism, the Cdv system, was recently discovered in archaea from the Crenarchaeota phylum. Despite these findings, division mechanisms remain to be identified in, for example, organisms belonging to the bacterial PVC superphylum, bacteria with extremely reduced genomes, wall-less archaea and bacteria, and in archaea that carry out the division process without cell constriction. Cytokinesis mechanisms in these clades and individual taxa are likely to include adaptation of host functions to division of bacterial symbionts, transfer of bacterial division genes into the host genome, vesicle formation without a dedicated constriction machinery, cross-wall formation without invagination, as well as entirely novel division mechanisms.