Archaeal cell cycle progress.

Abstract

The discovery of multiple chromosome replication origins in Sulfolobus species has added yet another eukaryotic trait to the archaea, and brought new levels of complexity to the cell cycle in terms of initiation of chromosome replication, replication termination and chromosome decatenation. Conserved repeated DNA elements--origin recognition boxes--have been identified in the origins of replication, and shown to bind the Orc1/Cdc6 proteins involved in cell cycle control. The origin recognition boxes aid in the identification and characterization of new origins, and their conservation suggests that most archaea have a similar replication initiation mechanism. Cell-cycle-dependent variation in Orc1/Cdc6 levels has been demonstrated, reminiscent of variations in cyclin levels during the eukaryotic cell cycle. Information about archaeal chromosome segregation is also accumulating, including the identification of a protein that binds to short regularly spaced repeats that might constitute centromere-like elements. In addition, studies of cell-cycle-specific gene expression have potential to reveal, in the near future, missing components in crenarchaeal chromosome replication, genome segregation and cell division. Together with an increased number of physiological and cytological investigations of the overall organization of the cell cycle, rapid progress of the archaeal cell cycle field is evident, and archaea, in particular Sulfolobus species, are emerging as simple and powerful models for the eukaryotic cell cycle.