47. for Escherichia coli chromosomal DNA replication, which one of the following statements is true?

(1) DNA polymerase I is the main polymerase required for DNA replication

(2) DNA polymerase I though identified originally by Kornberg as the one responsible for replication, is not important for the DNA replication process

(3) Requirement of DNA polymerase I is in the context of removal of RNA primer needed for DNA synthesis, and then fill in the same with DNA equivalent

(4) DNA polymerase I is the primary enzyme for error prone DNA synthesis in response to SOS.

Overview of DNA Polymerases in E. coli

Escherichia coli contains five DNA polymerases (Pol I, II, III, IV, and V), each with specialized roles:

• DNA polymerase III (Pol III): The primary enzyme responsible for the bulk of chromosomal DNA replication. It is a multi-subunit holoenzyme with high processivity and proofreading ability, synthesizing both leading and lagging strands.

• DNA polymerase I (Pol I): Functions mainly in processing Okazaki fragments by removing RNA primers and filling in the resulting gaps with DNA. It also participates in DNA repair.

• DNA polymerases II, IV, and V: Involved in DNA repair and translesion synthesis, with Pol IV and V being error-prone polymerases active during SOS response.

Evaluating the Given Statements

1. DNA polymerase I is the main polymerase required for DNA replication

   • Incorrect. Pol I is important for primer removal and repair but not the main replicative polymerase.

2. DNA polymerase I, though identified originally by Kornberg as the one responsible for replication, is not important for the DNA replication process

   • Incorrect. Pol I is essential for removing RNA primers and gap filling, a critical step in lagging strand synthesis.

3. Requirement of DNA polymerase I is in the context of removal of RNA primer needed for DNA synthesis, and then fill in the same with DNA equivalent

   • Correct. Pol I’s 5′→3′ exonuclease activity removes RNA primers, and its polymerase activity fills in the gaps with DNA.

4. DNA polymerase I is the primary enzyme for error-prone DNA synthesis in response to SOS

   • Incorrect. Error-prone synthesis during SOS is mainly carried out by Pol IV and Pol V, not Pol I.

Supporting Evidence

• The replicative polymerase in E. coli is DNA polymerase III holoenzyme, responsible for synthesizing the majority of DNA during replication.

• DNA polymerase I plays a specialized role in Okazaki fragment maturation, removing RNA primers and replacing them with DNA.

• DNA polymerase I also participates in DNA repair but is not the main replicative enzyme.

• Error-prone DNA synthesis during SOS response is mediated by specialized polymerases (Pol IV and Pol V), not Pol I.

Final Answer

(3) Requirement of DNA polymerase I is in the context of removal of RNA primer needed for DNA synthesis, and then fill in the same with DNA equivalent

Keywords

Escherichia coli DNA replication, DNA polymerase I, DNA polymerase III, Okazaki fragment processing, RNA primer removal, DNA repair, SOS response polymerases, DNA polymerase IV, DNA polymerase V, replicative polymerase

Summary:
In E. coli, DNA polymerase III is the main enzyme responsible for chromosomal DNA replication. DNA polymerase I is crucial for removing RNA primers from Okazaki fragments and filling in the resulting gaps with DNA. The error-prone DNA synthesis during SOS response is carried out by other polymerases, not DNA polymerase I.