What is the function of the sliding clamp PCNA in DNA replication?

• A. It acts as a processivity factor, forming a ring around DNA to hold polymerases in place and coordinate synthesis.
• B. It unwinds DNA at replication forks.
• C. It primes DNA synthesis by laying down RNA primers.
• D. It ligates DNA nicks after primer removal.

Answer: (C)

PCNA functions as a processivity factor during DNA replication. It forms a ring around the DNA strand, so it can encircle the template and physically tether DNA polymerases to the DNA. This keeps the polymerases from falling off after adding many nucleotides, allowing long, efficient synthesis. PCNA also serves as a docking platform, coordinating activities on the fork by interacting with multiple replication and repair enzymes to ensure smooth, coordinated synthesis on both the leading and lagging strands. It is loaded onto DNA by a clamp loader and then slides with the polymerase as replication proceeds. It does not unwind DNA (that’s the helicase’s job), it does not prime DNA synthesis (that’s done by primase), and it does not ligate nicks (that’s the role of DNA ligase).