Differential Effect of CLKs on HIV-1 Provirus Expression. Cells were transfected with CMVmyc 3xTerm (-) or CMVtTa (+, to induce endogenous HIV-1 provirus expression) along with control plasmid (CMVmyc 3xterm) or vectors expressing GFP-CLK1, GFP-CLK2, GFP-CLK3, GFP-CLK4, or the kinase-inactive form, GFP-CLK2 KR. Forty-eight hours post-transfection, media and cells were harvested and Gag (p24) protein levels determined by (A) p24 ELISA or (B) western blot. Shown are the averaged results of >5 independent assays with asterisks denoting results determined to significantly different from control (+tTA) at a p value of < 0.05. (C) As above but cells were transfected with increasing amounts of CLK2 expression vector. Media was harvested two days post transfection and HIV-1 Gag (p24) protein levels determined by ELISA. Shown is the average of multiple independent trials (N = 3).