Some archaeal chromosomes appear to have a single origin of replication whereas others have two or more origins. Homologs of some of the proteins involved in the initiation of eukaryotic DNA synthesis have been identified in archaeal genomes. However, different archaeal species appear to have ditftrent variants of the replication machinery components. These differences may reflect the great variation in environmental conditions under which the archaea live.

    Tne archaea produce a single protein, designated Ore1/Cdc6 which binds to the archaeal origin of replication. This protein share some sequences in common with the eukaryotic ORC. Once bound to the origin, Ore1/Cdc6 recruits MCM to the origin. The MCM helicase appears to work in the same way as the eukaryotic helicase. The helicase opens and unwinds the double-stranded DNA.

    RPA (single-stranded DNA binding protein) binds to the exposed single-stranded DNA.

    Primase associates with the RPA· DNA complex and synthesizes the short RNA primers required to initiate DNA synthesis. Then DNA polymerase associates with the replication bubble, initiating rapid and processive bidirectional DNA synthesis.