FIG 2.

Env determinants of differences in cold sensitivity between SHIV-89.6 and SHIV-KB9. (A and B) Residues in 89.6 Env that differ from those in KB9 Env were altered, alone or in combination, to those found in KB9 Env and vice versa. Recombinant luciferase-expressing HIV-1 pseudotyped with the designated Envs was incubated on ice for the indicated times, and infectivity was determined following incubation with Cf2Th CD4⁺ CCR5⁺ cells. Experiments were performed as indicated in the Fig. 1 legend. (C) The approximate ER_cold and ER_sCD4 values of the SHIV Envs used in this study are plotted. The red arrows indicate phenotypic changes that resulted from modifications of Env introduced in the laboratory. The green arrows indicate phenotypic changes that arose during passage of the virus in monkeys. Note that the ER_antibody of all the studied Envs is low.