DNA replication — processivity of polymerases Processive synthesis (addition of many nucleotides without dissociating) is most characteristic of which component during chromosomal replication?

Introduction:
Processivity measures how many nucleotides a polymerase adds before falling off the template. High processivity is critical for fast, accurate replication of long genomes. In bacteria, this property is conferred by specific proteins that tether the polymerase to DNA.

Given Data / Assumptions:

• Escherichia coli uses DNA polymerase III holoenzyme for bulk replication.
• The β sliding clamp dramatically increases processivity.
• Other steps like primer removal and repair generally require less processive enzymes.

Concept / Approach:

At the fork, the clamp loader (γ complex) loads the β clamp onto DNA, and Pol III core associates with it, enabling synthesis of thousands of nucleotides per binding event. By contrast, DNA polymerase I removes RNA primers with 5′→3′ exonuclease activity and is comparatively distributive.

Step-by-Step Solution:

Verification / Alternative check:

Single-molecule and biochemical assays show Pol III with β clamp synthesizes long stretches without dissociation, while Pol I adds relatively short patches.

Why Other Options Are Wrong:

Not all DNA polymerases are equally processive. Primer removal and mismatch repair involve short patch synthesis or excision, not sustained processive elongation. RNA polymerase pertains to transcription, not DNA replication processivity.

Common Pitfalls:

Assuming “polymerase” implies the same behavior across all enzymes; accessory factors like clamps dictate processivity.

Final Answer:

DNA polymerase III at a replication fork (with the sliding clamp)