The machinery required for the elongation stage of DNA synthesis in the arcnaea is very similar to that used by the bacteria and eukaryotes. Lagging and leading strand synthesis are coordinated. Processive DNA synthesis requires tethering DNA polymerase to a sliding clamp. The archaeal sliding clamp is similar in sequence and structure to PCNA in eukaryotes. The clamp loader appears to also be similar to its eukaryotic counterpart. Two different kinds of archaeal DNA polymerases, PolB and FolD, participate in the elongation process; however, not all archaeal species have PolB.

    It is not yet clearwhat specific contributions each of these polymerases make to DNA replication. Perhaps one participates in leading strand synthesis and the other in lagging strand synthesis. The archaeal counterparts of eukaryotic Fen-1 and RNase H remove RNA from the 5'-ends of the Okazaki fragments and DNA ligase joins the fragments. Archaeal ligase, like its eukaryotic counterpart, requires ATP for ligation. It therefore differs from the NAD+-dependent bacterial ligase.

    The archaeal replication system has one major surprise. Thermophiles require an ATP-dependent reverse gyrase to introduce positive supercoils. The reverse gyrase works by introducing transient nicks into a single strand and so functions by a different mechanism from the bacterial gyrase. Thermophiles may require reverse gyrase because they grow at high temperatures that tend to unwind DNA. Undoubtedly the archaeal replication machinery will have other surprises in store as we learn more about its components and how they work together. Perhaps the most remarkable surprise of all is how similar the replication process is in all three domains of life.