Figure 1: Schematic illustration of SAMHD1 protein and its functional domains. Numbers indicate amino acid positions of human SAMHD1 protein. The SAM domain, HD domain, and the C-terminal variable region of SAMHD1 are indicated. Other critical residues and motifs include nuclear localization signal (NLS), four critical residues in SAMHD1 NLS (11KRPR14), four residues in the enzymatic HD domain (H167, H206, D207, and D311), and phosphorylation of threonine at residue 529 (T592, indicated with the letter P).