ion of the C-terminal domains to be more flexible. This domain arrangement leads to the formation of an asymmetric homotetramer, rather than a symmetrical assembly, of the T. kodakarensis GINS.Cdc45 protein is ubiquitously distributed from yeast to human, supporting the notion that the formation of the CMG complex is universal in the eukaryotic DNA replication process. However, no archaeal homologue of Cdc45 has been identified. A recent report of bioinformatic analysis showed that the primary structure of eukaryotic Cdc45 and prokaryotic RecJ share a common ancestry. Indeed, a homolog of the DNA binding domain of RecJ has been co-purified with GINS from S. solfataricus . experiment detected the stimulation of the 5 - 3 exonuclease activity of the RecJ homologs from P. furiosus and T. kodakarensis by the cognate GINS complexes (Ishino et al., unpublished). The RecJ homolog from T. kodakarensis forms a stable complex with the GINS, and the 5 - 3 exonuclease activity is enhanced in vitro ; therefore, the RecJ homolog was designated as GAN, from GINS-Associated Nuclease in a very recent paper. related report found that the human Cdc45 structure obtained by the small angle X-ray scattering analysis (SAXS) is consistent with the crystallographic structure of the RecJ family members. These current findings will promote further research on the structures and functions of the higher-order unwindosome in archaeal and eukaryotic cells.
7. Primase
initiate DNA strand synthesis, a primase is required for the synthesis of a short oligonucleotide, as a primer. The DnaG and p48-p58 proteins are the primases in Bacteria and Eukaryota, respectively. The p48-p58 primase is further complexed with p180 and p70, to form DNA polymerase?-Primase complex. The catalytic subunits of the eukaryotic (p48) and archaeal primases, share a little, but distinct sequence homology with those of the family X DNA polymerases. first archaeal primase was identified from Methanococcus jannaschii, as an ORF with a sequence similar to that of the eukaryotic p48. The gene product exhibited DNA polymerase activity and was able to synthesize oligonucleotides on the template DNA. characterized the p48-like protein (p41) from P. furiosus . Unexpectedly, the archaeal p41 protein did not synthesize short RNA by itself, but preferentially utilized deoxynucleotides to synthesize DNA strands up to several kilobases in length. Furthermore, the gene neighboring the p41 gene encodes a protein with very weak similarity to the p58 subunit of the eukaryotic primase. The gene product, designated p46, actually forms a stable complex with p41, and the complex can synthesize a short RNA primer, as well as DNA strands of several hundred nucleotides in vitro . short RNA but not DNA primers were identified in Pyrococcus cells, and therefore, some mechanism to dominantly use RNA primers exists in the cells. research on the primase homologs from S. solfataricus , Pyrococcus horikoshii, and P. abyssi showed similar properties in vitro . Notably, p41 is the catalytic s...
