Question

A conditional mutation expresses its mutant phenotype only under certain conditions (the restrictive conditions) and expresses the normal phenotype under other conditions (the permissive conditions). One type of conditional mutation is a temperature-sensitive mutation, which expresses the mutant phenotype only at certain temperatures. Strains of E. coli have been isolated that contain temperature-sensitive mutations in the genes encoding different components of the replication machinery. In each of these strains, the protein produced by the mutated gene is nonfunctional under the restrictive conditions. These strains are grown under permissive conditions and then abruptly switched to the restrictive condition. After one round of replication under the restrictive condition, the DNA from each strain is isolated and analyzed. What characteristics would you expect to see in the DNA isolated from each strain with a temperature-sensitive mutation in its gene that encodes the following?a. DNA ligase

b. DNA polymerase I
c. DNA polymerase III
d. Primase
e. Initiator protein

Answer 1

a) DNA ligase

Due to temperature sensitivity DNA ligase action is impaired due to presence of multiple nicks but the DNA replication will proceed

b) Encoding polymerase I

Due to temperature sensitivity mutation occurs causing non-corrected strands to be obtained but DNA replication will continue

c) Encoding polymerase III

Replication is stooped here because of the importance of the enzyme in the synthesis of new strand

d) Primase

The enzyme will induce primers in forward and lagging strands

Step-by-step explanation:

DNA replication is facilitated by the functionality of enzymes in assisting the formation of new synthesis

Temperature sensitive mutations

a) DNA ligase

Due to temperature sensitivity DNA ligase action is impaired due to presence of multiple nicks but the DNA replication will proceed

b) Encoding polymerase I

Due to temperature sensitivity mutation occurs causing non-corrected strands to be obtained but DNA replication will continue

c) Encoding polymerase III

Replication is stooped here because of the importance of the enzyme in the synthesis of new strand

d) Primase

The enzyme will induce primers in forward and lagging strands

e) Initiator protein