![]() The second family of DNA-dependent DNA polymerases is DNA polymerase a (pol a) or B family DNA polymerase. Perhaps the best studied of these families is the DNA polymerase I (pol I) or A polymerase family, which includes the Klenow fragments of Escherichia coli and a Bacillus DNA polymerase I, Thermus aquaticus DNA polymerase, and the T7 RNA and DNA polymerases, all of whose crystal structures are known (3–11). From amino acid sequence comparisons (1) as well as crystal structure analyses (2), the DNA polymerases can be divided into at least five different families, and representative crystal structures are known for enzymes in four of these families. The crystal structures of numerous DNA polymerases from different families suggest that they all utilize an identical two-metalioncatalyzed polymerase mechanism but differ extensively in many of their structural features. Finally, all classes of polynucleotide polymerases must be able to translocate along the template being copied as synthesis proceeds. Further, these enzymatic scribes must faithfully copy the sequences of the genome into daughter nucleic acid or the information contained within would be lost thus some mechanism of assuring fidelity is required. Thus, one might anticipate that the mechanism by which all polymerases work would be both simple and universal. ![]() 552 refs.read more read lessĪbstract: Possibly the earliest enzymatic activity to appear in evolution was that of the polynucleotide polymerases, the ability to replicate the genome accurately being a prerequisite for evolution itself. Since there is in principle no difference in chemical catalysis by low-affinity compared to high-affinity metal sites, some of these enzymes are also included in this article, especially if they are or have been discussed as zinc enzymes, or are active with zinc. Another seemingly simple, yet experimentally sometimes complex issue concerns the choice of which metalloenzyme is a zinc enzyme. ![]() ![]() This means that, with a few exceptions, only zinc enzymes for which NMR or crystal structures are available are included here. In fact, the number of studies makes it impossible to provide a comprehensive review of the recent literature on zinc enzymology here, and the authors therefore focus on those zinc enzymes for which structure-function relationships are possible on the basis of structural and biochemical data. Abstract: Zinc enzymology is, compared to some other current areas of metallobiochemistry, a maturing field, but in addition to further developments of structure-function relationships it has also provided a number of surprising new results and ideas in the last few years. ![]()
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