1QSL:
reference: Structural elucidation of the binding and inhibitory properties of lanthanide (III) ions at the 3'-5' exonucleolytic active site of the Klenow fragment., Brautigam CA, Aschheim K, Steitz TA, Chem Biol 1999 Dec;6(12):901-8. PMID: 10631518

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