Which enzyme is responsible for replacing a nucleotide during base excision repair (BER)?

Base excision repair (BER) is a cellular mechanism that corrects DNA damage, specifically from small, non-helix-distorting base lesions. In this process, the first step is the recognition and removal of the damaged base by DNA glycosylase, which cleaves the bond between the base and the sugar-phosphate backbone, creating an abasic site.

Once the abasic site is formed, the next crucial step involves the replacement of the missing nucleotide. This is where DNA polymerase plays a key role. DNA polymerase is responsible for synthesizing new DNA by adding nucleotides complementary to the template strand. After the damaged base is removed and the abasic site is processed, DNA polymerase fills in the gap left by the missing nucleotide, effectively replacing it with the correct one.

Following the action of DNA polymerase, DNA ligase then seals the nick in the sugar-phosphate backbone to restore the continuity of the DNA strand. While other enzymes like DNA helicase are involved in the broader context of DNA replication and repair, their roles are not specifically related to the nucleotide replacement step in BER. Thus, DNA polymerase is the enzyme that directly catalyzes the incorporation of the correct nucleotide during the base excision repair process