You are studying the biochemistry of DNA polymerases in the bacterium X. coli. Y

Question

You are studying the biochemistry of DNA polymerases in the bacterium X. coli. You have discovered 3 distinct DNA polymerase activities D, F and G that you analyze in vitro. For these studies you have a single-strandeed DNA template made up of 3 regions A, C and B. In addition you have two single-stranded primers A' and B' that are complementary to A and B respectively (see below). Using the incorporation of radioactive nucleotide precursors as indicators of DNA synthesis and either primer A' or B' or no primer at all, you get the following results: a) Which DNA polymerase is similar to the E. coli DNA polymerase III? b) What are the properties of DNA polymerase G and how might its existence modify the present scheme of DNA replication? Be specific.

Explanation / Answer

Answer (a) :DNA polymerase G is similar to the E. coli DNA Polymerase III, as it contains two catalytic cores which replicates the DNA of both leading and lagging strands. The leading strand replication do not require primers.

(b): As the DNA polymerase G is similar to prokaryotic DNA polymerase III, it will have the following properties:

3’ – 5’ polymerase activity on lagging strand and 5’ – 3’ polymerase activity on leading strand.

3’ – 5’ exonuclease activity for proofreading.

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