Which enzyme helps relieve torsional strain ahead of the replication fork?

Topoisomerase is the enzyme that plays a crucial role in relieving torsional strain ahead of the replication fork during DNA replication. As DNA unwinds to allow for replication, it can introduce tension in the form of supercoiling. This torsional strain can hinder the progress of the replication machinery. Topoisomerases work by cutting the DNA strands, allowing them to unwind, and then resealing them, effectively removing the strain without disrupting the overall integrity of the DNA.

While helicase is responsible for unwinding the DNA helix, it does not address the torsional strain; instead, it primarily separates the strands of DNA. Primase synthesizes the RNA primer necessary for DNA polymerase to initiate replication, and ligase connects Okazaki fragments on the lagging strand, but none of these functions directly relieve the strain caused by unwinding DNA. Topoisomerase is specifically designed to manage these tension-related issues, making it the key enzyme in this context.