Polymerase and Histidinol Phosphatase domain of alpha-subunit of bacterial polymerase III DnaE3
PolIIIAs that contain an N-terminal PHP domain have been classified into four basic groups based on genome composition, phylogenetic, and domain structural analysis: polC, dnaE1, dnaE2, and dnaE3. The PHP (also called histidinol phosphatase-2/HIS2) domain is associated with several types of DNA polymerases, such as PolIIIA and family X DNA polymerases, stand alone histidinol phosphate phosphatases (HisPPases), and a number of uncharacterized protein families. DNA polymerase III holoenzyme is one of the five eubacterial DNA polymerases that is responsible for the replication of the DNA duplex. The alpha subunit of DNA polymerase III core enzyme catalyzes the reaction for polymerizing both DNA strands. The PolIIIA PHP domain has four conserved sequence motifs and contains an invariant histidine that is involved in metal ion coordination, and like other PHP structures, the PolIIIA PHP exhibits a distorted (beta/alpha) 7 barrel and coordinates up to 3 metals. Initially, it was proposed that PHP region might be involved in pyrophosphate hydrolysis, but such an activity has not been found. It has been shown that the PHP of PolIIIA has a trinuclear metal complex and is capable of proofreading activity. Bacterial genome replication and DNA repair mechanisms is related to the GC content of its genomes. There is a correlation between GC content variations and the dimeric combinations of PolIIIA subunits. Eubacteria can be grouped into different GC variable groups: the full-spectrum or dnaE1 group, the high-GC or dnaE2-dnaE1 group, and the low GC or polC-dnaE3 group.
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