Figure 3: SMR motif is necessary for CXCR4 downregulation. (A) Cell lysates of A3.01 T cells infected with each viral clone were analyzed 12 days post-infection for Nef expression level. Nef was found to be expressed in equal amounts in HIVNefsmr5a infected cultures as compared to HIVwt infected cultures. Image shown is a representative image from three independent experiments. (B-C) A3.01 T cells infected with HIVNefsmr5a, HIVwt, and HIVdsNef were analyzed for surface expression of CD4 and CXCR4 by flow cytometry. Mutation of the SMR motif abolished the ability of Nef to downregulate CXCR4. Nef-mediated downregulation of CD4 was slightly affected. Values reflect the means of three independent experiments, and error bars represent SEM of the mean. Differences between groups were determined using an unpaired student t-test *p<0.05, **p<0.01, ***p<0.001.