SAMHD1 and HIV-1 infection: Importantly, as soon as proliferating cells enter the G1 cell cycle-stage, HIV-1 infection resulted in significant reduction of RT products depending on the presence of SAMHD1 dephosphorylated at T592 (Fig. 7 and Supplementary Fig. 6d-i), while concomitantly dNTP levels are low (Fig. 1c; Supplementary Fig. 5c; Supplementary Fig. 6a-c).