6ig1
From Proteopedia
DNA polymerase IV - DNA ternary complex 10
Structural highlights
Function[DPO4_ECOLI] Poorly processive, error-prone DNA polymerase involved in untargeted mutagenesis. Copies undamaged DNA at stalled replication forks, which arise in vivo from mismatched or misaligned primer ends. These misaligned primers can be extended by PolIV. Exhibits no 3'-5' exonuclease (proofreading) activity. Overexpression of polIV results in increased frameshift mutagenesis. It is required for stationary-phase adaptive mutation, which provides the bacterium with flexibility in dealing with environmental stress, enhancing long-term survival and evolutionary fitness. May be involved in translesional synthesis, in conjunction with the beta clamp from PolIII.[1] [2] [3] [4] [5] Publication Abstract from PubMedDNA synthesis by DNA polymerases (dPols) is central to duplication and maintenance of the genome in all living organisms. dPols catalyze the formation of a phosphodiester bond between the incoming deoxynucleoside triphosphate and the terminal primer nucleotide with the release of a pyrophosphate (PPi) group. It is believed that formation of the phosphodiester bond is an endergonic reaction and PPi has to be hydrolyzed by accompanying pyrophosphatase enzymes to ensure that the free energy change of the DNA synthesis reaction is negative and it can proceed in the forward direction. The fact that DNA synthesis proceeds in vitro in the absence of pyrophosphatases represents a long-standing conundrum regarding the thermodynamics of the DNA synthesis reaction. Using time-resolved crystallography, we show that hydrolysis of PPi is an intrinsic and critical step of the DNA synthesis reaction catalyzed by dPols. The hydrolysis of PPi occurs after the formation of the phosphodiester bond and ensures that the DNA synthesis reaction is energetically favorable without the need for additional enzymes. Also, we observe that DNA synthesis is a two Mg2+ ion assisted stepwise associative SN2 reaction. Overall, this study provides deep temporal insight regarding the primary enzymatic reaction responsible for genome duplication. Pyrophosphate hydrolysis is an intrinsic and critical step of the DNA synthesis reaction.,Kottur J, Nair DT Nucleic Acids Res. 2018 Jul 6;46(12):5875-5885. doi: 10.1093/nar/gky402. PMID:29850882[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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