= Exonuclease
An <exonuclease> removes <nucleotides> from an end of a <nucleic acid>, in contrast to an <endonuclease> that cuts internal bonds. Direction, strand preference and <substrate> structure vary between <enzymes>. A proofreading <exonuclease> associated with some <DNA polymerases> can remove an incorrectly added terminal <nucleotide> before synthesis resumes. Consequently, exonucleolytic removal and polymerization can contribute to accuracy through different catalytic activities. <Molecular Biology of the Cell, 4th edition by Bruce Alberts and others>[Chapter 5, DNA Replication Mechanisms: proofreading exonucleases]{ref}
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