title: Initiation of DNA replication: functional and evolutionary aspects.
abstract: BACKGROUND
  The initiation of DNA replication is a very important and highly regulated step in the cell division cycle. It is of interest to compare different groups of eukaryotic organisms (a) to identify the essential molecular events that occur in all eukaryotes, (b) to start to identify higher-level regulatory mechanisms that are specific to particular groups and (c) to gain insights into the evolution of initiation mechanisms.
  
  
  METHODS
  This review features a wide-ranging literature survey covering replication origins, origin recognition and usage, modification of origin usage (especially in response to plant hormones), assembly of the pre-replication complex, loading of the replisome, genomics, and the likely origin of these mechanisms and proteins in Archaea.
  
  
  CONCLUSIONS
  In all eukaryotes, chromatin is organized for DNA replication as multiple replicons. In each replicon, replication is initiated at an origin. With the exception of those in budding yeast, replication origins, including the only one to be isolated so far from a plant, do not appear to embody a specific sequence; rather, they are AT-rich, with short tracts of locally bent DNA. The proteins involved in initiation are remarkably similar across the range of eukaryotes. Nevertheless, their activity may be modified by plant-specific mechanisms, including regulation by plant hormones. The molecular features of initiation are seen in a much simpler form in the Archaea. In particular, where eukaryotes possess a number of closely related proteins that form 'hetero-complexes' (such as the origin recognition complex and the MCM complex), archaeans typically possess one type of protein (e.g. one MCM) that forms a homo-complex. This suggests that several eukaryotic initiation proteins have evolved from archaeal ancestors by gene duplication and divergence.
authors.affiliation: Biosciences, College of Life and Environmental Sciences, Hatherly Laboratories, University of Exeter, Exeter, UK. j.a.bryant@exeter.ac.uk
authors.forename: John A
authors.initials: JA
authors.lastname: Bryant
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Aves
mesh_terms: D004261:DNA Replication / Q000187:drug effects / Q000235:genetics*; D018744:DNA, Plant / Q000235:genetics; D019143:Evolution, Molecular; D008954:Models, Biological; D010937:Plant Growth Regulators / Q000494:pharmacology; D018741:Replication Origin / Q000187:drug effects / Q000235:genetics
chemical_list: D018744:DNA, Plant; D010937:Plant Growth Regulators