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DNA Polymerase
Distant Relatives
All living organisms have DNA polymerases. Some, like the ones pictured here, are quite simple: one enzyme does it all. The ones in our own cells are more complex, composed of separate proteins that unwind the helix, build an RNA primer, and build the new strand. Some even have a ring-shaped protein that clamps the polymerase to the DNA strand. A single cell often has several different polymerases: complex ones that do the major DNA replication when the cell divides, and simpler ones that help in day-to-day repair and maintenance of the DNA.Three simple polymerases are pictured above, each with a tiny piece of DNA bound. In each picture, the template DNA strand is colored purple and the newly built strand is colored green. At upper left is DNA polymerase I from Escherichia coli, with PDB accession code 1kln. At upper right is human DNA polymerase, from the PDB file 1zqa. At bottom is a viral DNA polymerase, from the PDB file 1clq. The are quite different in size and shape, but notice how all wrap around the DNA, and enclosing the end of the DNA in a pocket in which the synthetic reaction is performed.
These illustrations were created with RasMol. You can create similar pictures by clicking on the accession codes, and then hitting "View Structure."
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Last changed by: A.Honegger,