FIGURE 1.

SAMHD1 is a dNTP triphosphohydrolase. PAGE analysis and activity assay of purified recombinant mouse and human SAMHD1 are shown. A, [³H]dATP (100 μm, 30,000 cpm/nmol) and 100 ng of mouse SAMHD1 were incubated for 0 or 20 min under assay conditions. After protein precipitation the reaction mixture was chromatographed isocratically together with nonlabeled carrier deoxyadenosine and dATP as detailed under “Experimental Procedures.” The graph shows the radioactivity of the reaction products in 0.5-ml fractions collected at the two time points. B, the same experiment is shown but with 300 ng of human SAMHD1. The insets show the electrophoretic analyses of 4 μg of each enzyme and the positions of molecular size markers.