Degradation of SAMHD1 by SIV Vpx and X-102. Increasing amounts of FLAG-tagged wild type and mutant SIV Vpx expression clones were co-transfected with FLAG-tagged SAMHD1 expression clones into 293T cells. After 72 hrs cell lysates were analyzed on PAGE-SDS and immunoblotted with anti-Flag and anti-Actin antibodies. Positions of SAMHD1, Actin, and Vpx in the blots are indicated. Densitometry values (normalized to levels of actin), relative to SAMHD1 in the absence of Vpx, are shown below each blot.