Figure 6. Ability of phosphomimetic and dimerization-defective SAMHD1 variants to block HIV-1 infection and decrease the cellular levels of dNTPs does not correlate with their ability to tetramerize and hydrolyze dNTPs in vitro.

(A) Total cellular levels of dGTP and dTTP were measured in PMA-treated U937 cells stably expressing SAMHD1 variants by using a primer extension assay, as described in Methods. (B) PMA-treated U937 cells stably expressing the indicated SAMHD1 variants were challenged with increasing amounts of HIV-1-GFP. Infection was determined by measuring the percentage of GFP-positive cells using flow cytometry.