FIG. 1.

(A) Construction of a Tax retroviral vector. The MuLV-based retroviral vector, pBabe-puro, was used to generate pBabe-Tax. A consensus Kozak sequence, GCCACC, was incorporated 5′ to the translational start codon of Tax. The complete coding sequence for Tax was then inserted into pBabe-puro via BamHI and EcoRI restriction sites. LTR, long terminal repeat. (B) Tax expression declines rapidly with passage in cell culture. Tax-transduced PA18G-BHK-21 cells were passaged every 4 to 5 days. Immunoblot analyses were carried out using 4C5 hybridoma supernatant and 50 μg each of total proteins from cells transduced with pBabe-puro (lane BHK-21) or pBabe-Tax harvested after serial passages (passage 0 to 3). Tax-expressing PX1 cells were included as a control (lane PX-1). Tax expression was detected 1 week following puromycin selection (passage 0).