DNA polymerase I has 5′-3′ polymerase activity, 5′-3′ exonuclease activity, and 3′-5′exonuclease activity necessary for DNA replication. Mutations in the gene that encodes DNA polymerase I may cause the enzyme to lose these activities.

Match the consequence of a loss‑of‑function mutation in DNA polymerase I to the corresponding lost activity.

a) Lost 5′-3′ polymerase activity

b) Lost 5′-3′ exonuclease activity

c) Lost 3′-5′exonuclease activity

1. No RNA primer removal during DNA replication

2. Decreased polymerase fidelity

3. No double helix denaturation

4. Unstable strand separation within the replication bubble

5. No DNA synthesis to fill gaps caused by removing RNA primers

DNA polymerase 1 has three sites, which provide three different catalytic activities: 3′ to 5′ exonuclease activity, 5′ to 3′ exonuclease activity, and 5′ to 3′ polymerase activity.

Mutations in the DNA polymerase 1 leading to lost 5'-3' polymerase activity is linked to no DNA synthesis to fill gaps that are maybe caused by the removal of RNA primers due to the lost ability of the polymerase activity to add nucleotides to growing strand.

Mutations in the DNA polymerase 1 leading to lost 5'-3' exonuclease activity is linked to no denaturation or no unstable strand separation within the bubble as this activity functions in polymerization activity to displacing DNA strands. However, the main function of the 5′ to 3′ exonuclease activity is to remove RNA primers that are utilized in DNA replication.

Mutations in the DNA polymerase 1 leading to lost 3'-5' exonuclease activity is linked to decreased polymerase fidelity as this exonuclease activity region is referred to as the proofreading or editing function of DNA polymerase I.