Archaeal DNA replication: Identifying the pieces to solve a puzzle

Archaeal organisms are currently recognized as very exciting and useful exp erimental materials. A major challenge to molecular biologists studying the biology of Archaea is their DNA replication mechanism. Undoubtedly, a full understanding of DNA replication in Archaea requires the identification of all the proteins involved. In each of four completely sequenced genomes, o nly one DNA polymerase (Pol BI proposed in this review from family B enzyme ) was reported. This observation suggested that either a single DNA polymer ase performs the task of replicating the genome and repairing the mutations or these genomes contain other DNA polymerases that cannot be identified b y amino acid sequence. Recently, a heterodimeric DNA polymerase (Pol II, or Pol D as proposed in this review) was discovered in the hyperthermophilic archaeon, Pyrococcus furiosus. The genes coding for DP1 and DP2, the subuni ts of this DNA polymerase, are highly conserved in the Euryarchaeota. Eurya rchaeotic DP1, the small subunit of Pol II (Pol D), has sequence similarity with the small subunit of eukaryotic DNA polymerase delta. DP2 protein, th e large subunit of Pol II (Pol D), seems to be a catalytic subunit. Despite possessing an excellent primer extension ability in vitro, Pol II (Pol D) may yet require accessory proteins to perform all of its functions in eurya rchaeotic cells. This review summarizes our present knowledge about archaea l DNA polymerases and their relationship with those accessory proteins, whi ch were predicted from the genome sequences.