Vpr induces less DNA damage than HIV-1 Vpr. (A) HeLa cells were transfected with HA-Vpr or SIVagm HA-Vpr expression vector. After two days, the cells were fixed, permeabilized and incubated with anti-γH2AX and anti-HA antibodies. Subsequently, the cells were stained with Alexa Fluor 594-anti-rabbit IgG and Alexa Fluor 488-anti-rat IgG. (B) The number of γH2AX dots in Vpr expressing cells was counted. More than 40 Vpr + cells were evaluated in each experiment. Control sample was transfected with pcDNA3.1 instead of Vpr expression vector. The data represent means with standard deviations from three independent experiments. P values were calculated by Student’s t-test with P < 0.05 considered as significant.