Aresearcher while working in vitro (outside cell) added helicase enzyme which resulted in the untwisting of the dna helix. but this untwisting led to strain ahead of the replication fork. which enzyme can be added to correct this problem? nuclease topoisomerase telomerase

The answer is Topoisomerase.

Topoisomerase is an enzyme with the role to regulate the overtwisting or undertwisting of DNA helix. If DNA helix is untwisted, topoisomerases will regulate this situation and will twist DNA helix.

Nuclease is an enzyme that cleaves the sequences of nucleic acids into smaller units.
Telomerase is an enzyme that adds specific sequence to the telomere ends.