Question

The effects of inhibitors of DNA synthesis can be studied in an in vitro replication

system containing E. coli enzymes. In this system replication of M13 DNA is

sensitive to the drug rifampicin, which inhibits host–cell RNA polymerase, but

replication of the E. coli cellular DNA is not.

a) What do these results suggest about the priming enzymes involved in the replication

of M13 DNA and E. coli DNA?

b) What would be the effect of a mutation disrupting the 5´-->3´ exonuclease

activity of DNA pol I on the replication of E. coli DNA?

Answer 1

A. The results suggest that E.coli cellular DNA does not use the RNA polymerase to produce RNA instead it uses its own enzyme that is called primase. But M13 uses host RNA polymerase to form primer and thus are rifampicin sensetive.

b.The 5'---->3' exonuclease activity of DNA pol I is needed to remove the RNA primers while the DNA is replicating. If the activity is removed due to mutation, the DNA replication machinery would stall ebfore the primer unable to remove the RNA primers.