SIVsmm nef alleles enhance viral infectivity. Infectivity of HIV-1 NL4-3 variants containing the indicated nef alleles. (A) P4-CCR5 or (B) TZM-bl reporter cells were infected with HIV-1 NL4-3 IRES-eGFP constructs containing the indicated HIV and SIVsmm nef genes or a disrupted nef allele. Infections were performed in triplicate with two different virus stocks containing 1 ng p24 antigen. RLU/s, relative light units per second. All nef alleles (except G932) significantly (P < 0.05) enhanced virion infectivity in P4-CCR5 but not in CEM-M7 cells.