FIGURE 2.

Fractions of ricin B chain can interact with BiP and lactose. A, protoplasts transfected with vector alone (vector), the RTB plasmid, or the γ-heavy chain of Guy's 13 immunoglobulin G plasmid (25) were radiolabeled with ³⁵S-amino-acids for 1 h before homogenization and IP with anti-RTB, anti-BiP, or anti-IgG antisera. IPs were washed in the absence (-) or presence (+) of ATP and analyzed by SDS-PAGE and fluorography. B, transfected cells were subject to pulse-chase before separated cell and medium homogenates were incubated with α-lactose immobilized onto agarose to select RTB with native conformation. Lactose-agarose pulldowns were analyzed by SDS-PAGE and fluorography. Numbers on the left indicate molecular mass markers in kilodaltons.