HTLV-I Tax physically interacts with both Spi-1 (A) and NF-IL6 (B). ³⁵S-labeled Tax and luciferase proteins were prepared by in vitro transcription and translation. Lanes 1 and 3 of experiments A and B indicated the mobilities of these radiolabeled proteins on SDS-PAGE. In lanes 2, 4, and 5 of A and B, labeled proteins were incubated with GST, GST-Spi-1, or GST-NF-IL6 protein linked to glutathione-agarose beads. After incubation, the beads were washed, and bound proteins were eluted. The eluted proteins were analyzed on SDS-PAGE.