SAMHD1 and HIV-1 infection: Interestingly, deletion of the N terminus, removing the conserved SAM domain in SAMHD1(113–626), resulted in a slight, yet reproducible enhancement of the ability of SAMHD1 to inhibit HIV-1 infection, which was relieved by Vpx, consistent with previous reports that this mutant is targeted for degradation by HIV-2/SIVmac Vpx, albeit less efficiently than full-length SAMHD1 (19–21, 37).