To ensure that the relatively large genomes of eukaryotic cells are efficiently and precisely duplicated in each cell cycle, DNA replication initiates from multiple replication origins distributed along the individual chromosomes. In budding yeast, replication origins are short, well-defined DNA sequences; in early metazoan development (e.g. Xenopus and Drosophila), regulated DNA replication can initiate from virtually any DNA sequence. The situation in somatic mammalian cells appears to lie somewhere between these two extremes. In most eukaryotic cell types,replication origins are activated continuously throughout S phase according to a temporal programme. For simplicity, an early-firing and a late-firing origin are considered in this poster, which summarises data from a variety of eukaryotic systems (for details, see Kelly and Brown,2000).FIG1
Step 1. Replication origins are determined, at least in part, by the binding of the six subunit origin recognition complex (ORC), which has been conserved in evolution from yeast...
