FIG. 3.
Expression of HTLV-1 Env TM truncation mutants and their incorporation into virions. Equal amounts of cell extracts were obtained from 2 × 106 to 5 × 106 293T cells cotransfected with 8 μg of an MLV-based lacZ reporter gene vector, 4 μg of the MLV p/CLGag-Pol expression vector, and 4 μg of either an HTLV Env-derived expression vector (H, HdC8, HdC16, or HΔC) or a control vector (Mock). The different HTLV Env TM mutants are diagrammed in Fig. 2. Cell extracts were immunoblotted with the 5a anti-HTLV TM monoclonal antibody (3) (left panel). Pelleted virions were obtained from supernatants of 293T transfectants after concentration by ultracentrifugation on a 20% sucrose cushion. Resulting pellets were immunoblotted with either the 5a anti-HTLV TM monoclonal antibody (anti-TM, center panel) or the 1C11 anti-HTLV SU monoclonal antibody (anti-SU, right panel). Respective levels of virion expression were controlled by immunoblotting with the R187 anti-MLV capsid monoclonal antibody (a kind gift of B. Chesebro) (anti-CA, center panel). The positions of the HTLV-1 Env precursors (Pr Env), mature TM, and mature SU envelope proteins are indicated.