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 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

ANSWER A :-

1. From the above mentioned data, it is clear that the E.coli is the host and the Bacteriophage M13 is the cell which is infecting the host. This uses the host genetic machinery to replicate and transcribe its genome.
2. The M13 phage has a single stranded DNA and is usually replicated in the presence of the RNA Polymerase whose activity is associated with DNA Polymerase.
3. RNA Polymerase is involved in formation of a primer sequence by means of which a new strand is being synthesized. Hence, this indicates the importance of the RNA Polymerase in the process which is specifically carried out by DNA Polymerase enzyme of the host. Rifampicin is a drug which inhibits the activity of RNA Polymerase thereby inhibiting the synthesis and linking of the Primer sequence to the M13 DNA thereby restricting its replication process.
4. This suggests the interactions between the RNA Polymerase enzyme and the drug Rifampicin to have an inhibitory effect on DNA Replication.

ANSWER B :-

1. RNA primer is basically a sequence of RNA and hence if it is not removed from the DNA strand, it will interfere with the sequence and may be associated with creating gaps which may remain vacant and prove deleterious.
2. Mutation in the exonuclease activity of DNA Polymerase may be associated with two changes either the Primer sequence may not be removed from the 5'-end or if removed may not be replaced by DNA sequence which in turn leads to errors during DNA Replication.

NOTE :- Respected Sir/Madam, for any doubts, please prefer communicating through the comment section.