Chapter 11: Conceptual Learning Activity
8. Interpret the data - Characterizing a viral DNA polymerase
DNA polymerases are an essential component of prokaryotic cells and eukaryotic cells. They are also an essential component of DNA viruses, because these viruses contain a DNA-based genome that must be replicated in order for the virus to replicate.
Bacteriophage 29 is a DNA virus that infects certain species of bacteria. The specific DNA polymerase from this virus is called 29 DNA polymerase. When researchers began to characterize 29 DNA polymerase in the early 1990s, they observed the following properties:
Property 1: It is highly efficient, carrying out thousands of polymerizations without detaching from the template.
Property 2: It can initiate DNA synthesis by attaching a nucleotide to the -OH group of a protein.
Property 3: It not only has 5'->3' polymerization activity but also 3'->5' exonuclease activity.
Property 4: It can unwind parental double-stranded DNA, enabling it to use one of the strands as a template.
These observations were surprising because the DNA polymerases of prokaryotic and eukaryotic cells exhibit only which one of these four properties?
The remaining three properties are not observed in cellular DNA polymerases. For example, consider Property 2. Cellular DNA polymerases cannot initiate the synthesis of a new strand by attaching the first nucleotide to a protein. Instead, they attach the first nucleotide to a short segment of RNA produced by a protein called. In order to better understand the source of these unique properties, researchers attempted to solve the molecular structure of 29 DNA polymerase. This goal was achieved in 2004 using X-ray diffraction studies.
