Which characteristics of DNA polymerase I raised doubts that its in vivo function is the synthesis of DNA leading to complete replication?

Verified step by step guidance

1. Understand the primary known activities of DNA polymerase I, which include its 5' to 3' polymerase activity, 3' to 5' exonuclease proofreading activity, and 5' to 3' exonuclease activity.
2. Recognize that DNA polymerase I has relatively low processivity, meaning it can add only a limited number of nucleotides before dissociating from the DNA template.
3. Note that DNA polymerase I's 5' to 3' exonuclease activity allows it to remove RNA primers but also limits its ability to synthesize long stretches of DNA continuously.
4. Consider that the enzyme's slower rate of DNA synthesis compared to other polymerases suggests it is not the main enzyme responsible for rapid and complete DNA replication.
5. Conclude that these characteristics—low processivity, presence of 5' to 3' exonuclease activity, and slower synthesis rate—raised doubts about DNA polymerase I being the primary enzyme for complete DNA replication in vivo.

Key Concepts

DNA Polymerase I Enzymatic Activities

DNA Polymerase I possesses multiple enzymatic functions, including 5' to 3' polymerase activity, 3' to 5' exonuclease proofreading, and 5' to 3' exonuclease activity. The presence of the 5' to 3' exonuclease allows it to remove RNA primers, but its relatively slow polymerization rate compared to other polymerases raised questions about its role in complete DNA replication.

Processivity of DNA Polymerase I

Processivity refers to the number of nucleotides a polymerase can add before dissociating from the DNA template. DNA Polymerase I has low processivity, meaning it frequently dissociates, which is inefficient for synthesizing long DNA strands required for complete replication, suggesting it may not be the main enzyme for this task.

Role of DNA Polymerase I in DNA Replication vs. Repair

While DNA Polymerase I can synthesize DNA, its primary in vivo role is believed to be removing RNA primers and filling short gaps during DNA repair and Okazaki fragment processing. This specialized function contrasts with the high-speed, high-processivity synthesis needed for complete genome replication, implicating other polymerases in that role.