Which enzyme is responsible for proofreading new nucleotide sequences for correctness?

DNA polymerase II is the enzyme responsible for proofreading new nucleotide sequences during DNA replication. This enzyme plays a crucial role in synthesizing new strands of DNA by adding nucleotides complementary to the template strand. During this process, DNA polymerase II has a built-in proofreading function that allows it to check for base-pairing errors as nucleotides are added. If an incorrect nucleotide is incorporated, DNA polymerase II can recognize the mismatch and remove it using its exonuclease activity before continuing with DNA synthesis. This proofreading capability significantly increases the fidelity of DNA replication, reducing the frequency of mutations.

In contrast, DNA ligase is primarily involved in joining Okazaki fragments during DNA replication, RNA polymerase synthesizes RNA from a DNA template during transcription, and helicase unwinds the double helix structure of DNA, facilitating replication and transcription. While these enzymes play critical roles in nucleic acid processes, they do not possess proofreading functionality like DNA polymerase II does.