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Samhd1 Is A Single-Stranded Nucleic Acid Binding Protein With No Active Site-Associated Nuclease Activity., Kyle J. Seamon, Zhiqiang Sun, Luda S. Shlyakhtenko, Yuri L. Lyubchenko, James T. Stivers

Journal Articles: Pharmaceutical Sciences

The HIV-1 restriction factor SAMHD1 is a tetrameric enzyme activated by guanine nucleotides with dNTP triphosphate hydrolase activity (dNTPase). In addition to this established activity, there have been a series of conflicting reports as to whether the enzyme also possesses single-stranded DNA and/or RNA 3'-5' exonuclease activity. SAMHD1 was purified using three chromatography steps, over which the DNase activity was largely separated from the dNTPase activity, but the RNase activity persisted. Surprisingly, we found that catalytic and nucleotide activator site mutants of SAMHD1 with no dNTPase activity retained the exonuclease activities. Thus, the exonuclease activity cannot be associated with any …