Structure
The structure for most DNA polymerases found in nature is
largely similar, with minor difference from organism to organism. The
first structure of a member from this family of enzymes studied was
E.Coli DNA polymerase 1. It was found that the polymerase domain had a
structure resembling that of a hand, with a palm, fingers, and a thumb.
The active site was located in palm portion. It is thought that Taq
polymerase shares a very similar structure, as shown in the figure
below:
The complete Taq DNA polymerase gene has 2499 base pairs. The enzyme itself
consists of 832 amino acid residues and has a molecular weight of
93910 Da.
It is thought that the increased thermostability of Taq polymerase
results
from its amino acid sequence (primary structure.) In particular, it has
a high Arginine to Lysine ratio when compared to polymerases obtained
from other sources. For example, the Arginine to Lysine ratio for Taq
polymerase is almost twice as that for E.coli
polymerase. This high ratio might in turn be a result of the high GC
content of thermophilic organisms. As we have learned in class, high GC
content is typical of Z-DNA and causes the DNA to be more extended and
stable. It it thus characteristic of organisms that thrive in hot
environments.
During replication, seven
absolutely conserved amino acid residues make contact with the template
DNA. Six of these are shown in the picture above; Arg 573, Tyr 671, Asn
750, Gln 754, His 784, and Asp 785
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