the short primer, and is therefore the main player of the DNA replication process. Based on the amino acid sequence similarity, DNA polymerases have been classified into seven families, A, B, C, D, E, X, and Y. fundamental ability of DNA polymerases to synthesize a deoxyribonucleotide chain is widely conserved, but more specific properties , including processivity, synthesis accuracy, and substrate nucleotide selectivity, differ depending on the family. The enzymes within the same family have basically similar properties. E. coli has five DNA polymerases, and Pol I, Pol II, and Pol III belong to families A, B, and C, respectively. Pol IV and Pol V are classified in family Y, as the DNA polymerases for translesion synthesis (TLS). In eukaryotes, the replicative DNA polymerases, Pol? , Pol? , And Pol? , Belong to family B, and the translesion DNA polymerases,? ,? , And? , Belong to family Y. most interesting feature discovered at the inception of this research area was that the archaea indeed have the eukaryotic Pol?-Like (Family B) DNA polymerases. Members of the Crenarchaeota have at least two family B DNA polymerases. On the other hand, there is only one family B DNA polymerase in the Euryarchaeota. Instead, the euryarchaeal genomes encode a family D DNA polymerase, proposed as Pol D, which seems to be specific for these archaeal organisms and has never been found in other domains. genes for family Y-like DNA polymerases are conserved in several, but not all, archaeal genomes. The role of each DNA polymerase in the archaeal cells is still not known, although the distribution of the DNA polymerases is getting clearer. first family D DNA polymerase was identified from P. furiosus, by screening for DNA polymerase activity in the cell extract. The corresponding gene was cloned, revealing that this new DNA polymerase consists of two proteins, named DP1 and DP2, and that the deduced amino acid sequences of these proteins were not conserved in the DNA polymerase families. P. furiosus Pol D exhibits efficient strand extension activity and strong proofreading activity. family D DNA polymerases were also characterized by several groups. The Pol D genes had been found only in Euryarchaeota. However, recent environmental genomics and cultivation efforts revealed novel phyla in Archaea: Thaumarchaeota, Korarchaeota, and Aigarchaeota, and their genome sequences harbor the genes encoding Pol D. A genetic study on Halobacterium sp . NRC - 1 showed that both Pol B and Pol D are essential for viability. interesting issue is to elucidate whether Pol B and Pol D work together at the replication fork for the synthesis of the leading and lagging strands, respectively. According to the usage of an RNA primer and the presence of strand displacement activity, Pol D may catalyze lagging strand synthesis.
Thaumarchaeota and Aigarchaeota harbor the genes encoding Pol D and crenarchaeal Pol BII, while Korarchaeota encodes Pol BI, Pol BII and Pol D. Biochemical characterization of these gene products will contribute to research on the evolution of DNA polymerases in living organisms. hypothesis that the archaeal ancestor of eukaryotes encoded three DNA polymerases, two distinct family B DNA polymerases and a family D DNA polymerase, which all contributed to the evolution of the eukaryotic replication machiner...
